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project-title,email,principal-investigator,co-investigators,estimated-vla-hours,estimated-gbt-hours,estimated-vlba-hours,project-summary,brief-project-description,special-resources-required,explain-why-the-project-cannot-be-submitted-as-a-large-proposal
Xmarx ™ Information Systems,info@9won1.com,Desia Yamese Clements Lewis,,0,0,0,The purpose of Xmarx ™ Project Bridging the Gap between Natural and Environmental Disasters in the Mining Industry.,"Through modification to the Xmarx ™ Information Systems (device) to receive warning notification of only irregular activity detected through the data retreived at station.

""Terminal/Station"" sends a notification of warning for irregular activity detected by data to Xmarx ™ Information Systems (""Device"").

Triggering audible and visual alerts from the Xmarx ™(""Device""), located at affiliated oil rigg/well and or ore mine, within area(s) of disastrous threat.

Proactive

During the event of a dropped ""null"" signal from Xmarx™ (""Device""), Emergency Facilities will receive simultaneously ""no communication"" message and respond by immediately sending rescue teams for identified latitude/longitude coordinates.

Through achieved results by cooperative sources of synergies, the possibility of decrease of catrophy, saved lives and intervene environmental/natural disasters, cause by human and industrial activity.","Additional Teammates, additional components, with contract of mutual agreement","There are so many industry sectors that can benefit from the ""system"" and more importantly the Earth."
The Jansky-Very Large Array Deep Extragalactic Cosmology Survey (V-DECS),m.l.brown@manchester.ac.uk,Michael Brown,"Eric Murphy, Matt Jarvis, Russ Taylor, Steve Myers, Ian Heywood, Philip Appleton, Lee Armus, Richard Battye, Stefi Baum, Philip Best, Sanjav Bhatnagar, William Brandt, Stefano Camera, Peter Capak, Tzu-Ching Chang, Tracy Clarke, James Condon, Vandana Desai, Jim Dunlop, Bryan Gaensler, Keith Grainge, Jenny Greene, Gulay Gurkan Uygun, Chris Hales, Martin Hardcastle, Ian Harrison, George Heald, George Helou, Jacqueline Hodge, Huib Intema, Rob Ivison, Neal Jackson, Preshanth Jagannathan, Mark Lacy, Joseph Lazio, Rachel Mandelbaum, Kim McAlpine, Prina Patel, Isabella Prandoni, Huub Rottgering, Lawrence Rudnick, Wiphu Rujopakarn, Eva Schinnerer, Frank Schinzel, Douglas Scott, Nick Scoville, Ian Smail, Oleg Smirnov, Vernesa Smolcic, Jeroen Stil, Michael Strauss, Dan Smith, Jean-Luc Starck, Mattia Vaccari, Tessa Vernstrom, Chris Willott, Jonathon Zwart",3500,0,0,"We propose to use the J-VLA to conduct an ambitious, 6-year public Legacy Program that will uniquely address key science themes of our generation including the nature of dark energy, the evolution of galaxies & AGN, and the role of magnetic fields in galaxies, AGN & large scale structure. These questions can only be addressed through very deep observations over a sufficiently large sky area, leading to a proposal to map 10 sq. degs. in well-studied extragalactic fields down to 1.5 micro-Jy/bm at 3 GHz, primarily in A-configuration. V-DECS will be the first radio survey to deliver a statistically significant measurement of weak lensing by large-scale structure, a key probe of dark energy physics. We forecast a 5-sigma detection of the lensing signal in the radio, while the ability to cross-correlate with the rich overlapping optical data in these fields will facilitate a 15-sigma detection of the radio-optical cross-correlation lensing signal. With an expected 100,000 (1,000) source detections in total intensity (polarization), V-DECS will also facilitate major advances in understanding AGN & galaxy evolution at high redshift, and in unveiling the role of magnetism over cosmic time.","The J-VLA Deep Extragalactic Cosmology Survey (V-DECS) will survey 10 sq. degs. of sky down to 1.5 micro-Jy/bm at 3 GHz. The survey will cover the extended COSMOS and ELAIS-N1 fields, which benefit from exquisite existing multi-wavelength coverage, in particular, the HST-ACS coverage on COSMOS and the Hyper Suprime-Cam (HSC) survey deep field observations. In addition to the availability of ancillary data relevant to the V-DECS key science goals, the field choice is also motivated by more logistical/practical considerations, including the beam quality necessary for weak lensing measurements, RFI and scheduling concerns. While many types of ancillary data are valuable in support of V-DECS observations, HSC deep field imaging along with deep Spitzer IRAC and additional ground-based optical and near-infrared data are considered essential for identifying galaxy counterparts to faint, high-z radio sources. There are also compelling synergies with the deep LOFAR survey of the ELAIS-N1 field, which is forecast to reach a depth of 15 micro-Jy in 2019, which, for steep spectrum sources is comparable to this proposal.

The observations will be mostly conducted in A-configuration, complemented with more compact configurations to sample the relevant spatial scales of galaxies at all cosmic epochs (approx. 16:4:1 in total integration time for configurations A:B:C). The survey will build on the existing J-VLA 3 GHz observations of the COSMOS field (which cover 2 sq. degs down to 2.3 micro-Jy/bm). V-DECS will facilitate a broad range of extragalactic science, and for many science applications, will be the premier radio dataset until Phase 1 of the Square Kilometer Array (SKA) comes online in the late 2020’s. In particular, V-DECS will remain the only radio survey that can resolve star-forming galaxy (SFG) disks at z~1 over a significant cosmological volume until the advent of the SKA. To ensure a lasting impact, V-DECS makes optimal use of the J-VLA's unique capabilities: (i) high resolution imaging and exquisite point-source sensitivity, critical for resolving distant galaxies and proper source identification; (ii) wide bandwidth coverage, enabling instantaneous spectral index determination; and (iii) full polarimetry, enabling instantaneous rotation measure and Faraday structure determinations. Below we highlight the three main science drivers that serve as the foundation for the entire survey, each of which exploit these unique capabilities. However, the full suite of science applications that will be born out of V-DECS is undoubtedly beyond what we can envisage at this stage.

1. Probing the Dark Universe with Radio Weak Lensing and Large Scale Structure

The nature of dark energy, and gravity on large scales, remain major outstanding questions in cosmology. Weak gravitational lensing (or “cosmic shear”) – the effect whereby images of faint, distant background galaxies are coherently distorted by intervening large scale structures – is recognized as one of the key probes that will allow us to constrain dark energy and modified gravity theories. V-DECS will play a critical role in extending this science area to radio surveys. Its combination of excellent sensitivity and high angular resolution (both of which are essential for weak lensing) will remain unsurpassed until the advent of the SKA. Given the current SKA timescale, the first results from a large SKA weak lensing survey are unlikely to appear before ~2030.

Weak lensing with the full SKA represents a so-called “Stage-IV” dark energy experiment, on the same level as the LSST, Euclid and WFIRST-AFTA lensing surveys. Each of these Stage-IV experiments are sufficiently statistically powerful that controlling systematic errors (due to both astrophysical and instrumental effects) to the level required for precision dark energy constraints is a major outstanding challenge. Radio weak lensing has unique features, not available in the optical band, that can be used to mitigate these systematics. These unique features include the stable and deterministic point spread function (PSF) of an interferometer, the smooth power law spectra that galaxies typically exhibit in the radio band, and radio polarization information which provides a unique way to measure the intrinsic shapes of distant galaxies. By exploiting these advantages, and combining them with overlapping optical observations, radio surveys have the potential to maximize the scientific gain of weak lensing, and provide the most robust cosmological constraints. However, in order to realize these huge potential benefits, an innovative pathfinding experiment is needed to develop and hone the novel techniques required, and to drive the growing radio weak lensing community forward. With its unique combination of area, resolution and depth, V-DECS is the ideal survey to fulfill this pioneering role.

Based on measured source counts, and on our recent weak lensing analysis of the existing 3 GHz J-VLA COSMOS data, we forecast that V-DECS should facilitate a robust 5-sigma detection of the cosmic shear signal from the radio data alone. Such a result would be game-changing for the field of radio weak lensing – the current best radio-only measurement is a marginal (~3-sigma) detection using the FIRST survey. Moreover, given the existence of high quality, overlapping optical data from HST and the HSC surveys, V-DECS will also facilitate an unprecedented measurement of the radio-optical cross-correlation cosmic shear signal, with a forecasted detection significance of ~15-sigma. Again, this can be compared to the current best results which are a ~3-sigma detection from a FIRST/SDSS cross-correlation analysis and a ~2-sigma result from the combined analysis of the existing 3 GHz JVLA and HST data in the COSMOS field. While the forecasted precision of the V-DECS measurement is much smaller than that expected from state-of-the-art optical surveys (e.g. HSC surveys & DES), such precision comparisons completely ignore the impact of systematics, which, as described above, is the key strength of radio weak lensing. In this respect, V-DECS will demonstrate the unique and potentially ground-breaking advantages of radio weak lensing, on real data, for the first time. In addition to weak lensing, the 10 sq. degree V-DECS survey will allow a precise measurement of the bias of radio galaxies with respect to the underlying dark matter distribution. This is an important measurement that can be used to understand the role that larger-area radio continuum surveys (e.g. VLASS and future SKA surveys) can play in testing the cosmological principle and general relativity on the largest observable scales.

2. A Complete Census of AGN and Star Formation Activity over Cosmic Time

Understanding AGN “feedback” (thought to regulate star-formation in massive galaxies) is a key goal of galaxy evolution studies and there is now strong evidence that the standard AGN unification paradigm does not give a complete picture. For example, observational evidence suggests that many or most low-power radio galaxies in the local Universe correspond to a distinct type of AGN. These sources accrete through a radiatively inefficient mode (the so-called “radio mode”), rather than the radiatively efficient “quasar mode” typical of radio-quiet AGN. The role of these two accretion modes appears to be strongly influenced by the environment, while the level of radio-jet activity appears to be a strong function of the stellar mass of the host galaxy.

Investigating the nature of feedback and the accretion mode dichotomy can only be achieved with large, statistically complete samples of radio sources, with excellent, homogeneous multi-wavelength data. While shallow-wide radio surveys currently provide a reasonable baseline of radio AGN at low redshifts, a survey such as V-DECS is required to push detections of classical radio-loud AGN down to the realm of radio-quiet AGN at 1 < z < 2, where feedback needs to be most active to prevent galaxy growth. The depth and breadth of V-DECS will enable unique studies of the entire AGN population from z~1 to z~6, providing a complete view of nuclear activity in galaxies and its evolution, unbiased by gas/dust selection effects. For example, V-DECS will be unique in its ability to measure HERG/LERG populations as a function of redshift, stellar mass, star-formation rate (SFR) and environment up to redshifts, z~3. Specifically, we expect to detect a factor of ~8 more low-accretion rate radio sources at z > 1 than the current VLA-COSMOS data is capable of. This will facilitate an accurate measurement of the evolution of such sources, and will allow us to pin-down the amount of energy deposited into the intergalactic medium by such objects over the whole era of their activity.

In almost all existing large-scale radio surveys (including the ongoing VLASS), the vast majority of the sources detected are the accretion-dominated AGN. However, the SFG population begins to contribute to the source counts at 1.4 GHz flux densities around 1 mJy/bm, growing to dominate at fainter flux densities. Surveys of the cosmic SFR as a function of epoch suggest that the SFR density rises as (1+z)^4 out to at least z = 1 and then flattens, with the bulk of stars seen in galaxies today having been formed between z = 1 and 3, in the so-called epoch of galaxy assembly. However, the effect of dust on the
traditional optical and UV measurements of the SFR means that the behavior of the cosmic SFR density at redshifts above z~1 is still uncertain. This is exacerbated by the effects of cosmic variance in the current samples (multi-wavelength surveys such as COSMOS and GOODS typically cover only modest-sized areas, ~2 sq. degs., corresponding to just ~50 Mpc at z = 2), as well as small sample sizes. Given that star-formation is dependent on both host stellar mass and environment, any investigation of the evolution of SFGs requires the ability to detect them over a significant range in stellar mass and cosmic environments (e.g., from rich clusters to voids), as well as cosmic epoch.

V-DECS is ideal for tracing the cosmic history of star-formation, as a function of stellar mass, environmental density and epoch, without being hindered by significant sample variance or dust extinction biases. It is designed to detect SFGs out to z = 4, and will detect ~50,000 over the full 10 sq. degs. (compared to ~5500 in VLA-COSMOS). The combination of V-DECS J-VLA array configurations and relative sensitivities ensures that we will obtain complete flux-density limited samples, where we detect the emission on all
spatial scales associated with galaxies beyond the local (z < 0.1) Universe.

A further exciting application will be first measurement of the interplay between environment, AGN activity and the total star-formation in dark-matter halos, as a function of radio power and redshift. Such a study would link in perfectly with studies conducted over similar areas using optical and near-infrared data, where we are now seeing an unexpected relationship between the star formation activity in neighboring dark matter haloes, so-called galactic conformity.

3. The Deep Polarized Sky: The Evolution of Cosmic Magnetism

V-DECS will precisely measure the evolution of galactic-scale magnetic fields over cosmic time, a fundamental aspect of the polarized universe that is currently poorly constrained. It will achieve this by measuring the position angle of the integrated
polarized radiation for an unprecedented number of high-redshift SFGs. Recent observations show that at least 60% of unresolved normal spiral galaxies are polarized higher than 1%, and in some cases higher than 10%. Based on simulations calibrated
against these observations, with V-DECS we expect to detect polarized emission from several 10s of such disk galaxies in each square degree, sampling to redshift z~2. In the presence of an ordered large-scale galactic magnetic field, the integrated polarization is expected to be aligned with the minor axis of the galaxy for rest-frame frequencies above a few GHz. The V-DECS frequency range (2 – 4 GHz) makes it the ideal survey for observing this correlation – at lower frequencies, the effects of internal Faraday rotation from the galactic ISM both depolarizes the radiation and breaks the global symmetry of the observed field. This analysis will allow tests of proposed galactic magnetic field generation mechanisms, with which we can provide the first constraints on the time scales for galactic magnetic field amplification and the strength of the initial seed fields.

By providing a high density grid of Rotation Measures (RM) as background probes, V-DECS also presents an exciting opportunity to detect intergalactic magnetic fields (IGMFs) associated with the large scale structure of the Universe. Lambda-Cold Dark Matter (LCDM) cosmology predicts a cosmic web of galaxy clusters and filaments. While clusters contain hot plasma at T > 10^7 K, filaments are filled with cooler plasma at 10^7 > T > 10^5 K, and are expected to be significantly magnetized. However magnetic fields in filaments have not yet been detected due to the expected very low value 1 - 100 nG. Simulations show that RM grids with sky density greater than 100 per square degree, and RM precision of a few rad/m^2, are required to detect and reconstruct the structure function of RM variance due to the IGMF in the cosmic web. The number density of sources with polarized intensity above 15 mJy in V-DECS will be ~200 per sq. deg. At this intensity, the precision of the RM values will be better than 10 rad/m^2, thus offering our first good chance to detect the presence of weak magnetic fields associated with large scale structure.

Finally, V-DECS will also uniquely sample the polarization properties of faint, low-luminosity AGN in the radio flux density regime where radio emission from star-formation competes with the central AGN activity. Extrapolating from existing results, we expect that a significant fraction of the 100 - 200 polarized sources per square degree that V-DECS will detect, will include radio emission from AGN. Such a dataset is essential for understanding a number of outstanding problems in AGN models, e.g. the observed anti-correlation of polarization fraction with source flux density, and the dependence of this correlation on source structure, radio luminosity, redshift and/or environment. For example, there are suggestions that the larger polarization fractions seen in fainter sources may be related to accretion mode. More generally, the V-DECS polarization observations will allow valuable statistical characterizations of different AGN populations, and the first statistical studies of depolarization effects across the 2 - 4 GHz band, as a function of luminosity, redshift and environment.","Given the enormous resource that the V-DECS dataset will offer to the entire astronomical community, we are proposing that V-DECS be conducted as a Public Legacy program, with the data being available in the NRAO archive immediately, with no proprietary period. We have put together a team of multi-wavelength experts, including members of the HSC team and a
number of radio astronomy experts who are heavily involved with SKA scientific and technical planning. Consequently, we have the expertise in hand to ensure that this program reaches its full scientific potential. Like VLASS, we will make a number
of basic data products available to the community in a timely manner. The Basic Data Products of V-DECS consist of the: raw visibility data; calibration data and scripts to generate calibration products; single-epoch images and image cubes; single-epoch
basic object catalogs; cumulative images and image cubes; and cumulative catalog. We plan to work with NRAO to make use of existing resources for processing, curating, and serving the basic data products. We additionally have team members with the expertise and hardware in place to handle the data reduction and analysis independent of NRAO resources.

Beyond the resources needed to host the data, V-DECS is a multi-cycle, multi-configuration proposal, and the Observatory will need to give careful consideration of how the V-DECS observations can be accommodated into the overall J-VLA observing
schedule over the anticipated 6-year duration of the survey. Scheduling, observing and QA of the V-DECS observations themselves will be handled by members of the V-DECS team on a rotating basis.

The V-DECS team will also take responsibility for the production of higher-level science products. Examples include: full-Stokes, A-projection corrected image cubes; Multi-frequency synthesis average-band total intensity image sets; Faraday dispersion/Rotation Measure synthesis cubes; Galaxy shear catalogues, Polarisation source catalogues and Q, U spectra for source components; Improved object catalogs; and Catalogs of multi-wavelength associations and photometric redshifts to V-DECS sources. The immediate utility and lasting legacy of V-DECS requires a visible and robust archive. While the raw data will be served by NRAO, we will also make the above enhanced data products available to the astronomical community. We propose to locate this V-DECS archive at IRSA/IPAC. IRSA has an extensive user base that includes a large swathe of astronomers, and ingests enhanced
contributed products from other missions, such as Spitzer, Herschel, and Planck. Indeed, the public COSMOS data are hosted at IRSA, as are the Spitzer data taken in ELAIS-N1, and Herschel data for both fields, making it a natural home for V-DECS as well. Finally, IRSA is one of NASA’s Astrophysics Archives, making it much more robust in the long term compared with an unaffiliated website.","During 2015–2016, a group of more than 200 multi-wavelength astronomers worked to develop a next-generation large radio survey (the Very Large Array Sky Survey; https://science.nrao.edu/science/surveys/vlass) that would showcase the unique capabilities of the upgraded J-VLA). The final proposal, which included a Deep imaging component, underwent careful examination via internal NRAO and external Community Reviews, for which all materials (the proposal, technical implementation plan, review presentations, and the reports) can be found at https://safe.nrao.edu/wiki/bin/view/JVLA/VLASS.

While the headline science of the Deep component was extremely well received by the Community Review (with e.g. the weak lensing science case judged to be one of the top three science cases out of the entire VLASS proposal), it nevertheless recommended that the Deep tier component of VLASS should be declined as it was judged to be (i) not fully optimized for the headline weak lensing science case and (ii) not well-suited to a “community” survey. The Community Review’s final recommendation, which was prompted by their considerations of the VLASS Deep component, was for NRAO to implement a mechanism for reviewing, scheduling and supporting very large PI-led J-VLA programs, a recommendation that NRAO are now exploring through this X-proposal EoI call.

The current V-DECS proposal is the revised VLASS Deep proposal that was anticipated in the Community Review report, where we have further optimized the survey strategy to align with the primary weak lensing science case (by removing the low declination E-CDF survey field, which is not well suited for weak lensing, and concentrating observations on the higher declination COSMOS and ELAIS-N1 fields). V-DECS is well suited to the X-proposal mechanism for exactly the reasons stated in the VLASS community report. In particular, the very large time request, and the multi-cycle, multi-configuration nature of V-DECS make it near-impossible for it to be fairly assessed through the normal Large Proposal mechanism as it will always be perceived to be too large and too risky in comparison to smaller proposals."
MOJAVE: Parsec-Scale Magnetic Field Evolution of AGN Jets,mlister@purdue.edu,Matthew Lister,"Dan Homan, Ken Kellermann, Yuri Kovalev, Tuomas Savolainen, Alexander Pushkarev, Margo Aller, Hugh Aller, Talvikki Hovatta, Jose-Luis Gomez",0,0,1728,"We propose a NRAO X program to investigate the parsec-scale magnetic field evolution in powerful jetted outflows associated with active galactic nuclei (AGN). By obtaining monthly VLBA 15,22, and 43 GHz images of a sample of 50 AGN jets for a period of three years, we will obtain invaluable data on the 3D structure of the magnetic field and jet magnetization, velocity, collimation profile, and stratification at the highest angular resolution for comparison with the latest generation of fully relativistic MHD jet simulations. Our program will build on the highly successful MOJAVE program, which has operated continuously on the VLBA since its inception in 1994, and in full polarization since 2002. As is currently the case for MOJAVE, fully reduced data and images from the project will be made public within six weeks of correlation, providing an important resource and legacy archive for the AGN community. The monitoring sample contains a wide cross-section of AGN jet classes, chosen for their transversely resolved jet structure, bright polarized emission, and membership in many other multi-wavelength monitoring programs.","MOJAVE (Monitoring of Jets in AGN With VLBA Experiments) is a high impact large VLBA program that makes regular observations of the most compact AGN jets in the northern sky at 15 GHz. It began as the VLBA 2cm Survey in 1994, and since 2002 has provided full polarization
imaging and astrometric data on over 400 AGNs. Many individual sources have continuous monitoring baselines spanning 25 years, which has led to considerable new insights into the kinematics of highly relativistic outflows powered by supermassive black holes. Through the
study of complete radio- and gamma-ray flux-limited samples, MOJAVE has answered many outstanding questions regarding secular changes in AGN jet flows, has determined the distribution of jet speeds in the radio-loud AGN population, and has identified strong links between low- and high-energy emission in blazars. Having achieved these major milestones, we propose to introduce a new set of science goals that will lead to a much better understanding of the magnetic field structures in AGN jets, as well as the dense material located in the nucleus of their host galaxies.

At the beginning of the MOJAVE program, numerical simulations lagged behind the observations, but the situation has now reversed itself. Our new proposed VLBA observations will provide invaluable data on the 3D structure of the magnetic field and jet magnetization, velocity, collimation profile, and stratification at the highest angular resolution for comparison with our latest generation of fully relativistic MHD jet simulations (e.g., Fuentes et al. 2018). These show that the jet dynamics and emission properties depend mainly on the type of energy dominating the jet (internal, magnetic, or kinetic), the magnetic field structure and jet stratification, and the particle injection mechanism. Our science goals will be achieved by transitioning the MOJAVE program to more frequent simultaneous multi-frequency VLBA imaging at 15,22, and 43 GHz of a smaller, well-selected sample of 50 AGN jets. As we describe below, this will represent a doubling of the current VLBA time devoted to MOJAVE, bringing it into the X-proposal range.

Currently, the MOJAVE VLBA observational scheduling is optimized to track slow changes in total intensity structure and jet direction, and to determine the speeds and accelerations of bright jet features. Each jet is observed at a particular cadence, ranging from once per month to once per year, depending on the angular speeds of its jet features, such that they can be well-tracked across the epochs. With an observational allotment of one 24 hr VLBA session per month for the last several years, we have been able to effectively monitor approximately 100 jets at any given time with adequate interferometric coverage and image S/N ratio. Our linearly-interpolated time-lapse movies (http://www.physics.purdue.edu/astro/MOJAVE/movies.html) show smooth changes in total intensity, but in polarization it is evident that changes happen on much faster timescales, especially in the innermost few milliarcseconds of the jets \citep{2007ApJ...659L.107D}. It is currently unclear how much of this is due to intrinsic changes in the jet magnetic field structure, and/or changes in a foreground Faraday screen of plasma just outside the jet.

In order to address these issues, we require multi-frequency observations at a higher cadence, such that both total intensity and polarization variations, as well as the polarization rotation measure and spectral index can all be tracked simultaneously. To date this has been done for only short periods (< six months) on two AGN jets (e.g., 3C 273 \citealt{2008ASPC..386..451S} and 3C 120 \citealt{2011ApJ...733...11G}). These successful studies indicate that monthly observations, with all frequencies observed simultaneously, are necessary to smoothly connect the variations across the epochs and obtain reliable rotation measure maps. They also highlight the importance of having sufficient angular resolution to mitigate beam depolarization effects, which can be achieved by observing at the highest VLBA frequencies (15 GHz and above). The wide variety of jet speeds, accelerations, and polarization characteristics seen in the MOJAVE AGN sample underscores the need to observe a large sample of jets at high cadence in order to identify and understand general trends. Another major finding obtained from stacking MOJAVE images taken over several years is that at any given epoch, only the currently energized portion of the parsec-scale jet is detectable in VLBI images. What may appear as a highly bent flow in a single epoch image is readily recognizable as a smooth conical jet in the stacked-epoch image (e.g., \citealt{2017MNRAS.468.4992P}). This means that multi-year monitoring is essential for fully understanding the structure and evolution of the flow.

We propose a VLBA X-program to obtain monthly observations of 50 AGN jets in full polarization at 15, 22 and 43 GHz. Three frequencies are the minimum required to obtain reliable spectral index and rotation measure maps. The sample will be selected from the MOJAVE survey as having sufficient flux density for direct fringe detection at 43 GHz, transversely-resolved jets (to probe Faraday rotation gradients across the jets), and bright polarized downstream emission. Some of our targets will overlap with the Boston University sample, which is monitoring 33 AGN monthly with the VLBA at 43 GHz. Our sample will contain a much wider range of AGN classes, including low, intermediate, and high-spectral peaked blazars, and some gamma-ray quiet AGN.

Half the sample will be scheduled in each session, such that each jet is observed monthly. We prefer 24 hour sessions as this will accommodate the full 24 R.A. range spanned by the sample, and in our experience has provided the most efficient means of polarization calibration, using the target sources themselves as leakage and fringe calibrators. With 25 targets per session, this optimizes the S/N required for polarization imaging at all 3 frequencies without sacrificing excessive overhead to antenna slewing.

We propose a three year duration for the project, in order to fully sample slow changes in the energized portions of the jet, to adequately track the slower moving jet features, and to study jet accelerations. In our most recent MOJAVE kinematics analysis paper, we find that most jet
features have angular speeds below 0.2 mas/y, implying that they move through only a fraction of a 15 GHz VLBA beamwidth per year. Although the positions of bright features can be determined to within a few tens of microarcseconds, proper tracking of their accelerations (which are typically on the order of 10 to 100 microarcsec/y) requires a multi-year continuous dataset. The other reason for a 3 year duration is to continue the community legacy aspect of the MOJAVE program. For the last two decades, we have made our fully reduced data publically available on our project website within six weeks of correlation. This has provided a valuable and unparallelled resource for researchers interested in particular blazars that are the subject of multi-wavelength campaigns or of other special interest (such as the recently identified high-energy neutrino source TXS 0506+056; http://arxiv.org/abs/1807.07942 ). In addition to the 76 MOJAVE team papers, this has resulted in MOJAVE data being used in over 130 publications by authors not affiliated with the MOJAVE team https://www.cv.nrao.edu/2cmsurvey/publications2.html) . We also note that our sample of 50 blazars contains a large fraction of the most heavily monitored blazars at wavelengths ranging from radio to TeV energies. (http://www.physics.purdue.edu/astro/MOJAVE/blazarlist.html)",Disk space on the CV public web server to continue to host the MOJAVE public data archive.,"Our proposal belongs in the X category due to its large legacy aspect and interest to the AGN community,and the large total time request (two 24 hour VLBA sessions per month for 3 years, with half the sample observed in each session, i.e., 2x24x12x3 = 1728 hours) spread over multiple proposal cycles. In order to achieve the scientific goals, the project additionally requires permanent high-priority status in the VLBA dynamical queue, enabling it to obtain bi-monthly observations with reasonably good weather for 43 GHz observing at a minimum of 8 VLBA sites, which must include both SC and MK to achieve sufficient angular resolution."
POETRY: Pursuit of Extragalactic Transients with the VLA,eberger@cfa.harvard.edu,Edo Berger,"Kate Alexander
Iair Arcavi
Peter Blanchard
Damiano Caprioli
Poonam Chandra
Shami Chatterjee
Ryan Chornock
Deanne Coppejans
Philip Cowperthwaite
Maria Drout
Paul Duffell
Tarraneh Eftekhari
Ryan Foley
Wen-fai Fong
Bryan Gaensler
Suvi Gezari
Dimitrios Giannios
Sebastian Gomez
Cristiano Guidorzi
James Guillochon
Andy Howell
Nuria Jordana
Dan Kasen
Stefanie Komossa
Tanmoy Laskar
Andrew MacFadyen
Ben Margalit
Raffaella Margutti
Brian Metzger
Dan Milisavljevic
Dae-Sik Moon
Carole Mundell
Matt Nicholl
Kerry Paterson
Rosalba Perna
Eliot Quataert
Enrico Ramirez-Ruiz
Andy Read
Armin Rest
David Sand
Richard Saxton
Patricia Schady
Lorenzo Sironi
Gregory Sivakoff
Giacomo Terreran
Hendrik van Eerten
Sjoert van Velzen
Ashley Villar
Peter Williams",1350,0,0,"Time-domain astronomy is a rapidly-growing field focused on the study of energetic transient phenomena that mark diverse explosive end-points of stellar evolution, the birth and demise of compact objects, and the formation of jets and outflows. These processes manifest across the electromagnetic spectrum, and now in gravitational waves. The field is in the midst of a golden era, with thousands of transients discovered each year, providing both large statistical samples and new rare events. Radio follow-up provides unique and powerful insight not available from the discovery data, thereby allowing us to study common fundamental processes that underlie seemingly disparate types of events: formation of outflows and jets, shocks and particle acceleration, and the ambient environments of the transients. We propose the first extensive post-upgrade VLA program to uniformly study a wide range of transient phenomena taking advantage of the VLA's unmatched angular resolution, sensitivity, and spectral coverage. The program will provide a powerful complement to radio transient discoveries by VLASS and will delineate the path for time-domain science in the ngVLA and LSST era.","We propose an extensive program of Jansky Very Large Array follow-up of a diverse set of extragalactic transient events (e.g. supernovae, gamma-ray bursts, tidal disruption events, gravitational wave mergers), with the goals of uncovering and delineating common physical processes such as jet and outflow formation and particle acceleration, as well as uniquely probing the ambient environments of the relevant physical systems (massive stars, neutron star binaries, supermassive black holes) on otherwise inaccessible physical scales. The various transient events play a major role in the broad astrophysical context: they pinpoint the diverse end-points of stellar and binary evolution; they are responsible for synthesizing a wide range of elements, spanning the entire periodic table; they inject energy into the interstellar medium of their host galaxies and therefore influence star formation and feedback; they give birth (or represent the demise) of diverse compact objects; they probe otherwise dormant supermassive black holes; and they provide the connection between electromagnetic and gravitational wave radiation. The transient events studied in this program will be selected from a large data stream generated by wide-field surveys in the optical, X-ray/gamma-ray, and gravitational waves. Most importantly, in all of these cases the radio observations will provide unique insight that is not available from the discovery data itself, while at the same time the discovery datasets (and supporting multi-wavelength observations) will provide the critical context for interpreting the radio data.

We will obtain VLA target-of-opportunity observations spanning timescales of hours to months, and will collect an unparalleled large sample of events, focusing on both the best-studied examples of common types of transients (e.g. supernovae) and the rarest and most newly-discovered (e.g. gravitational wave events). We propose a 3-year 1350-hour program that will span a critical phase in the field: the transition to the unprecedented time-domain data streams from LSST and from wide-field radio time-domain surveys (ASKAP, SKA), and the build-up to design sensitivity of gravitational wave detectors. The dataset collected with this program will produce three critical legacies: (1) it will provide unprecedented insight into the most fundamental common physical processes in astrophysical transients; (2) it will provide unique insight into the progenitor systems, their evolutionary history, and their physical environments; and (3) it will delineate the best approaches for time-domain studies with the VLA and ngVLA in the next decade and beyond.

Over the past two decades the VLA has been at the forefront of time-domain studies, and has been utilized to study various types of transients, starting with a focus on supernovae and gamma-ray bursts, and more recently events like tidal disruptions of stars by supermassive black holes and gravitational wave sources. Following its upgrade the VLA is unmatched in transient follow-up thanks to the combination of angular resolution, sensitivity, and frequency coverage that no other radio interferometer offers. These characteristics, rather than wide field imaging, are the most critical for follow-up of individual events so no other facility could provide the data set needed for this program.

In all of the diverse astrophysical systems that we will target with this program the radio emission probes the presence and properties of ejected matter and its interaction with the ambient medium of the progenitor system. The radio emission is generally produced via shocks (relativistic or non-relativistic) as the ejected matter slams into the surrounding medium, on scales that are otherwise unresolvable at the relevant extragalactic distances (i.e., less than a parsec). The detailed properties of the radio emission, such as its spectral energy distribution and time evolution, therefore depend on the mass, velocity, and geometry of the ejected matter, as well as the density and profile of the ambient medium. In turn, these shed direct light on the processes by which matter is ejected and on the nature of the progenitor system.

On the other hand, the emission in the discovery bands for the various transients (mainly optical for supernovae and tidal disruption events, gamma-rays/X-rays for GRBs, gravitational waves for compact object mergers) is due to other processes, and the combination of these data with radio observations is particularly powerful. For example, in supernovae the optical emission is due to radioactive decay of nickel synthesized in the explosion, and therefore probes a distinct set of processes that are unrelated to the matter ejection that can instead be probed with radio observations. The combination of the two can therefore produce a complete picture of the explosion. Similarly, the optical emission in supernovae (or gamma-ray emission in GRBs, etc.) provides no insight about the local environment, which can serve as a powerful clue about the nature of the progenitor system. Radio observations provide this insight across a wide range of transient events. This provides us with a view of the state of the progenitor systems and their environment leading up to their demise.

At the same time, using radio follow up of transients discovered at other wavelengths has the advantage of providing a framework for the interpretation of the radio data. While the radio emission from a GRB or a tidal disruption event jet may appear similar in terms of its radio properties, the fact that the discovery data tell us the type of event provides a context for understanding the formation of the jet and drawing conclusions about the mechanisms at work. In this manner, our proposed program complements the on-going VLASS (and other efforts such as LOFAR, MWA, ASKAP) to discover transients directly through their radio emission. In the latter, the focus is on finding radio phenomena that may or may not produce emission at other wavelengths, while here the focus is on studying transient radio emission in a physical context provided by discovery at other wavelengths. In part, the mapping of the range of radio emission in the various transients from our proposed program will provide a context in which to interpret radio transients discovered in, for example, VLASS.

The previous radio follow-ups have paved the way for a uniform and coherent eXtra Large Program to study transient events. We have now found evidence for fast outflows and jets in a diverse set of transients, but mostly based on individual events; most recently, for example, we found shown that the first binary neutron star merger produced a relativistic jet similar to those in short GRBs. It has thus become clear that studying each class of transients in isolation is limiting progress in the field. Namely, the fact that different events are discovered with different surveys and techniques has inhibited our ability to uncover the common physical processes that underlie these various types of transients. Instead, we require a uniform approach to studying the radio emission, and hence common physical processes, in a broad set of transients.

Fortunately, the timing for such a program is ripe. The field of time-domain astronomy has recently entered a golden era in which a wide range of transients are discovered with diverse techniques in unprecedented numbers. A large number of wide-field optical surveys, utilizing a range of observational approaches is now producing a discovery rate of about 1 transient per hour (up from a handful per week only a few years ago). Satellites like Swift and Fermi are finding hundreds of GRBs per year, and gravitational wave detectors are finally discovering compact object mergers after decades of planning and construction. These large discovery streams have two advantages. First, they provide large statistical samples that can fully capture the range of behavior in common types of transients (e.g., supernovae). Second, they are able to discover rare types of never before seen events. Radio follow-up of both types is critical. In the case of large statistical samples, this means that we can focus on the best-studied events which have extensive datasets in the discovery band and at other follow-up bands, and hence a legacy value in the field. At the same time, we will focus on new and rare types of transients, which will provide new insight into the diverse end points of massive stars and binary systems.

In all cases the proposed VLA observations will be supported by extensive multi-wavelength datasets collected and analyzed by members of our team; we have assembled a group with years of expertise across the full range of astrophysical transients to facilitate coordinated follow-up and analysis. The events studied in this program will therefore offer the most complete and broad view of transient events to date. Based on past experience we anticipate about 10-20 hours of VLA time to study each transient event at multiple epochs and frequencies, and on timescales of days to months. Thus, with an allocation of about 450 hours per year spread over 3 years, we will be able to produce a legacy sample of about 100 transient events spread across a wide range of physical systems. The VLA's dynamic scheduling is particularly well matched to this program, providing the flexibility to target new events as they are discovered, and to monitor previous events. The longer timescale of the program compared to the normal proposal cycle will also mean that we can ensure follow-up of long-lasting events, as well as guard against semester-to-semester variation in event rates.

Looking forward, the next decade of time-domain astronomy will undergo even broader expansion, with LSST producing over a million transients in its decade-long survey, a full network of gravitational wave detectors, and wide-field radio time-domain surveys. At the same time, we anticipate that the VLA will transition into the ngVLA phase, with significantly enhanced sensitivity. The proposed program will therefore not only produce its own legacy data products, but will also inform the best strategies for radio time-domain astronomy in the next decade.

To achieve the goals of this program we have assembled a large international team of researchers with a broad set of expertise. In this way our team includes access to both proprietary and public data streams from which we will select events for VLA follow-up, as well as expertise in collecting and analyzing those data to produce a complete picture for each event. Similarly, our team includes personnel with broad experience in radio time-domain astronomy, spanning the full range of transients that will be targeted with this program. Finally, we involve most of the leading theorists in the field to both help with the interpretation of the data, as well as to provide targeted numerical simulations and analytical models to explain individual events. We believe that this broad constituency of astronomers will help to cement to the legacy value of this VLA program, as well as to provide a streamlined framework in which to disseminate new results and insight. Given the scope of the program and its anticipated long-term impact we will make reduced data products available in real-time. We will take advantage of the deep expertise in radio data analysis of various team members, as well as efforts such as CIRADA, which is being used to generate transient alerts from the VLASS.","We will take advantage of the VLA's dynamic scheduling to follow-up a wide range of astrophysical transients, with an average allocation of about 40 hours per month for 3 years. For some of the observations we will require rapid data processing to inform the details of subsequent VLA observations. This will necessitate access to local computing resources at NRAO to eliminate the time delay associated with large data transfers. However, we anticipate that this will only be required for <20% of the collected data since longer term follow-up will be carried out on timescales of days to months. In some cases we will require sub-array observations to simultaneously collect data at 2-3 frequencies (for example, to probe interstellar scintillation).","The current SRP/TAC time allocation process for time-domain target-of-opportunity studies requires rigid trigger and follow-up criteria that adversely impact the ability to draw connections and insight from the wide range of known and newly-discovered transient phenomena. In particular, it inhibits critical work on processes at the intersection of various phenomena (for example, relativistic outflows that manifest in gamma-ray bursts, some supernovae, tidal disruption events, and gravitational wave sources). Past and on-going programs have focused on rigidly defined types of events, and hence lacked the ability to uniformly study the relevant processes across a range of systems. This has also inhibited the ability to rapidly respond to new and unanticipated discoveries (which have instead been dealt with non-uniformly through director's discretionary time allocations). We have reviewed the last 3 years of time-domain programs at the VLA and found that with few exceptions the typical program has an allocation of only about 10-20 hours, is focused on a very narrow slice of events, and is designed to follow up only a few events. With such a fractured approach the follow-up is highly non-uniform for various types of transients, and progress in the field has been too slow and incremental.

An X-Proposal will alleviate all of these shortcomings. First, with a comprehensive allocation we will be able to uniformly follow up a large sample of transient across the full range of extragalactic systems. Second, a large allocation will allow us to collect sufficiently large samples for both the best studied cases of the more common types of transients, and for rare events. Third, with a large multi-year allocation we will be able to track the evolution of long-lasting events, as well as guard against semester-to-semester variations in the rate of rare events. Fourth, we will be able to uniformly study a wide range of transient phenomena, regardless of their specific method of discovery (optical, high energy, gravitational waves). Fifth, we will be able to rapidly advance the field in a short period of time and determine the best approaches for time-domain VLA/ngVLA studies in the LSST, SKA, full gravitational wave network era in the mid-2020s. None of these goals can be achieved under the current SRP/TAC time allocation process, for either regular or large programs."
Probing the 3.3 mm Confusion Limits,amroczko@eso.org,Tony Mroczkowski,"Jack Sayers
Itziar Aretxega
Alexandra Pope
Charles Romero
Simon Dicker
Nick Battaglia
Jon Sievers
Brian Mason",0,2592,0,"Wide, confusion-limited surveys at mm wavelengths are expected to constrain the very high redshift (z>3) population of dusty galaxies. To date, most deep mm-wave surveys have covered pencil beams, or have covered a few square degrees to a much shallower limit, while telescopes like Herschel have probed the 2<z<3 population at low resolution. The TolTEC camera -- which has 3 bands simultaneously probing 1.1, 1.4, and 2.0 mm -- on the 50-meter Large Millimeter Telescope (LMT) will change this, surveying a full square degree to the confusion limit in a 5-9.5 arcsec beam. We will propose to complement the TolTEC Ultra-Deep Survey (TUDS) with 3.3 mm observations using the 100-meter Green Bank Telescope and the MUSTANG-2 instrument. For typical dusty sources, we expect a confusion limit of 7 microJy/bm, roughly 3 times lower than the LMT at 2 mm (18 microJy/bm in a 9.5"" beam). We therefore will aim to cover a 20' by 20' portion of the TUDS region to the confusion limit in a survey totalling 1300 hours on sky. Much like Herschel constraints on the galaxy population at 2<z<3, we expect the TolTEC+MUSTANG-2 result to transform our understanding of dusty galaxy evolution.","We will propose to cover a 20' by 20' region or set of fields in the TolTEC Ultra-Deep Survey (http://toltec.astro.umass.edu/science_ultra_deep_survey.php) to the 3.3 mm confusion limit. The limit is expected to be ~7 microJy/bm at MUSTANG-2's 9"" resolution on the GBT, extrapolating from surveys at other wavelengths. Importantly, 3.3 mm is near the minimum in the contribution of radio and dusty mm/submm galaxy contamination, making confusion-limited observations particularly challenging. The limits obtained combining the MUSTANG-2 and TolTEC data will serve as a valuable pathfinder for future extragalactic and CMB surveys.

The TolTEC Ultra-Deep Survey working group has not yet determined the survey region. One potential set of fields would incorporate the HST Frontier Fields, which observed 6 clusters and 6 offset, blank sky regions. The clusters serve as ``cosmic telescopes,’’ both highly magnifying a few high-z galaxies as well as lowering the confusion limit in the cluster field, while the blank fields serve as unbiased survey regions. In the case that the Frontier Fields are selected, the MUSTANG-2 90 GHz measurements will additionally probe the SZ effect from the cluster foregrounds, and would serve as the deepest SZ maps of any cluster or set of clusters to date. The multifrequency coverage, including deep HST, VLA, ALMA, and TolTEC observations, will be crucial for disentangling the source signals and determining their origin.",Access to some of the best observing conditions for high-frequency work will be required.,"In order to cover 1/9 of the TolTEC Ultra-Deep Survey, we already require 2592 hours including overheads. A large proposal of only a few hundred hours would severely limit the size and/or depth of the survey, making it less competitive for cosmology and with complementary deep surveys already being carried out by ALMA."
Resolving atomic gas disks in the JINGLE galaxy sample,wilsoncd@mcmaster.ca,Christine Wilson,"Lihwai Li,
Aeree Chung,
Bumhyun Lee,
Elias Brinks,
Toby Brown,
Mark Sargent,
Ilse de Looze,
Angus Mok,
Sheona Urqhart,
Phil Cigan,
Martin Bureau,
Kijeong Kim,
Matt Smith,
Ji Hoon Kim,
Michal Michalowski,
Jillian Scudder",2000,0,0,"We propose to use the VLA to obtain sensitive, high resolution images of HI emission from the 193 galaxies in the JINGLE nearby galaxy sample. These data will resolve the atomic emission from the galaxy disks and will be combined with far-infrared and CO data to map the full content of the interstellar medium in star forming galaxies in field, group, and cluster environments.","The interstellar medium (ISM) plays a crucial role in the past and future evolution of star forming galaxies. While molecular gas provides the fuel for current star formation, the atomic phase dominates the dynamical state of the ISM in while also serving as a reservoir from which the molecular gas is replenished to balance depletion by star formation. Furthermore, at large galactic radii, HI rotation curves constrain the mass of dark matter in individual galaxies, while variations in the size and shape of the HI disk are amongst the best indicators of environmental influence.

JINGLE is a mass-selected sample of galaxies with far-infrared detections from the Herschel Space Observatory and a wealth of ancillary multi-wavelength data from ultraviolet to radio wavelengths (Saintonge, Wilson, et al. 2018, submitted). All 193 JINGLE galaxies have been mapped in dust emission at 850 microns with 15” resolution using the James Clerk Maxwell Telescope (JCMT); roughly half the JINGLE sample has or will be observed with a single pointing in the CO J=2-1 line with the JCMT as well. Optical IFU maps are available for half the galaxies from the MaNGA survey and for many of the remaining JINGLE galaxies from the SAMI or CALIFA surveys. Global HI fluxes are available from the ALFALFA survey (Haynes, Giovanelli, et al. 2018) or from a JINGLE follow-up program with Arecibo (de Looze, Smith et al., in prep). There is a pilot program to map 20 JINGLE galaxies in CO 2-1 at 7” resolution with the Atacama Compact Array and we plan to submit additional ACA proposals to observe a larger fraction of the sample. The JINGLE sample probes a range of environments from isolated galaxies to the massive Coma cluster.

Missing from this list of data is resolved information on the atomic gas content. Resolved maps of the atomic gas content of the JINGLE sample will greatly expand the range of science topics accessible with JINGLE. We will be able to measure the dust to gas mass ratio as a function of radius instead of simply global values. Combined with CO images, we will also measure the H2/HI mass ratio and compare it with radial trends in the star formation rate and molecular gas depletion time. Radial HI profiles can also be used to identify HI-deficient galaxies in groups and clusters. For example, Mok et al. (2017) found that star-forming galaxies in the Virgo cluster showed truncated HI radial profiles and enhanced H2 radial profiles, suggested of gas inflows triggered by interactions or ram pressure in the cluster environment. There are also strong synergies between resolved HI maps and optical IFU data, such as radial trends between HI content and gas-phase metallicity. Radial HI profiles also play a key role in distinguishing between inside-out and outside-in quenching of star formation in spiral disks.

The 193 galaxies in JINGLE can be mapped to a resolution of 6” (1.2-6 kpc for the range of distances in the JINGLE sample) and a sensitivity similar to that of the THINGS survey (Walter et al. 2008) with an integration time of 10 hours per galaxy. Observing for 1.5 hours in D array, 2.5 hours in C array, and 6 hours in B array will allow us to capture the full range of emission in all the JINGLE targets. For a velocity resolution of 5 km/s and assuming 3sigma detection across two velocity channels, these observations would have a column density sensitivity of 3.5E20 H/cm^2 or 3 Mo/pc^2, sufficient to detect HI emission across wide areas of the galaxy disks.

Such a survey would have a factor of 5 better angular resolution than HI surveys with the SKA precursor ASKAP (30” resolution). The MONGHOOSE large project on 30 nearby galaxies with MeerKAT uses 30” resolution to reach extremely high sensitivity, while the MeerKAT Fornax survey will have a maximum resolution of 10”.",Automatic flagging for RFI is probably the critical facility this project would need from the observatory. Pipeline calibration and imaging with auto-masking on observatory computing facilities would be very helpful in producing rapid science-quality images.,"We need 10 hours per galaxy for sufficient sensitivity and angular resolution, so for a sample of ~200 sources this project needs 2000 hours. We need to observe the full sample because strength of science comes from size and uniformity of the sample. We feel that a time request that is 10 times the minimum time required to qualify as a normal large proposal requires special evaluation and considerations and therefore is best suited to the new X-proposal process."
The complete multi-frequency VLA-COSMOS survey: Benchmarking radio continuum as,vs@phy.hr,Vernesa Smolcic,"Caitlin Casey, Jeyhan Kartaltepe, Eva Schinnerer, Peter Capak, Mark Sargent, Mladen Novak, Jacinta Delhaize, Kresimir Tisanic, Marco Bondi, Paolo Ciliegi, Gianni Zamorani, Ivan Delvecchio, Eleni Vardoulaki, Benjamin Magnelli, Daizong Liu, Philipp Lang, Eric Murphy, Chris Carilli, Nicholas Scoville, Hans-Rainer kloeckner, Kunal Mooley, Brent Groves, Huib Intema, Frank Bertoldi, Jacqueline Hodge, Matt Jarvis, Sarah leslie, Lana Ceraj, Eric Faustino Jimenez-Andrade, Kevin Harrington",2090,0,0,"One of the major quests in astrophysics is to understand how stellar mass (M*) builds up in galaxies through cosmic time. The radio window is unique by providing a dust-unobscured star formation tracer at high resolution. The power of large, deep radio surveys has been amply demonstrated, e.g. by our VLA-COSMOS Projects. Our latest results, probing the universe out to z~6, however, challenge key assumptions for the radio spectrum of typical star-forming galaxies with far-reaching implications for the determination of fundamental properties such as K-corrected radio luminosity and star-formation rate (SFR) at high redshift. We propose to benchmark radio continuum as a SFR tracer through cosmic time via multi-frequency radio coverage of 1.8 sq.deg. towards the COSMOS field, by building a unique radio dataset with the widest radio continuum coverage ever for a large deep field with excellent multi-wavelength coverage. We will deliver empirical calibrations of the conversion from radio continuum to SFR for a large parameter space in stellar mass, SFR, and redshift. This will provide the basis for next generation radio facilities, such as the ngVLA, and has a long lasting legacy value.","One of the major open questions in modern astrophysics is how stellar mass builds up in galaxies through cosmic time. This is directly linked to the star formation history of the universe.

Many in-depth studies in the past decade have rather well established the cosmic star formation history over the universe's last ~10.4Gyrs (z~2), even though a significant scatter between studies using different star formation tracers remains also at these redshifts. Moreover, star formation tracers and conditions for star formation at earlier cosmic times (z>2) are still highly uncertain, and many of them are biased against obscured, highly star-forming (likely massive) galaxies (e.g., Bouwens et al. 2015). Ideally one would use sensitive, high angular (~1"") resolution observations of dust unbiased star formation rate (SFR) tracers to determine the evolution of the cosmic star formation density and test the impact of dust onto its determination. Only radio and far-IR observations are ideal tools and major upgrade and the onset of new radio interferometers, the Karl G. Jansky VLA and ALMA, have only recently enabled such studies at early cosmic time (z>4; e.g., Dunlop et al. 2017; Novak et al. 2017).

With no compelling (far-)IR mission or instrument on the horizon, radio continuum provides the best tool in the coming decades. We are entering a 'golden age' of radio astronomy with the recent major instrument advancements (e.g. VLA, LOFAR, GMRT, with ngVLA and SKA being the most prominent future ones), bringing radio astronomy to the forefront of multi-wavelength research (e.g., Padovani et al. 2016). Disturbingly, our understanding of the (origin of the) radio spectral energy distribution is currently insufficient to fully exploit the extraordinary capabilities provided by these superb radio instruments. Our current lack of knowledge will severely hamper the interpretation of survey data arising from these instruments. Here we propose an empirical approach to remedy the situation.

The key goal of this proposal is to deliver robust empirical calibrations of the conversion from radio continuum to SFR including uncertainties as a function of observing frequency for an unprecedentedly large parameter space in stellar mass (9<logM/Ms<12) and SFR (1<SFR[Ms/yr]<5000) spanned by various galaxy populations over redshifts 0.3<z<6). The proposed observations will allow us to benchmark radio continuum luminosity as a robust star formation tracer through cosmic time by studying the evolution of the radio spectra of various populations of star forming galaxies out to z~6 using direct detections (z<2) and stacking methods (z>2).

Combination of the proposed observations of the COSMOS field at 6 & 10GHz with existing high quality radio data from 230MHz to 3GHz will provide a unique testbed for radio continuum emission as a star formation tracer well into the epoch of reionization. The very rich multi-wavelength database of the COSMOS field is essential to fully characterize the star-forming galaxy populations and link these to the average radio spectrum. The resulting unique multi-frequency radio coverage (e.g. Schinnerer et al. 2007, 2010, Smolcic et al. 2014, 2017) will both serve as a testbed and provide the currently missing basis required for next generation radio facilities such as the ngVLA.

Main science goal: Calibrating radio continuum as a star formation tracer over cosmic time

To establish radio continuum emission as a robust SFR tracer out to the highest redshifts (into the epoch of reionization), we need to understand on a fundamental level:

A/ What is the shape of the galaxy-integrated radio spectrum and how does it evolve with cosmic time and radio luminosity for a given galaxy population?

B/ What is the relation between radio continuum and star formation powered (far-IR) emission and how does it evolve with cosmic time as a function of galaxy population?

To address these burning questions we will utilize i) direct detections in multiple (N>=4) radio bands, mostly at z<2, and ii) stacking of stellar mass selected galaxy populations at z>2 from 230MHz to 10GHz, i.e. over almost 2 orders of magnitude in frequency. To make these simple, but fundamental measurements of the radio spectrum and investigating its relation to the (F)IR emission is essential to achieve the precision required for future studies of the cosmic star formation density with upcoming radio facilities.

Radio Spectral Energy Distribution (SED) & SFR Calibration

There is mounting evidence that the very well sampled radio SED of the nearby starburst galaxy M82 (e.g., Condon 1992), regularly taken as the typical radio SED for star forming galaxies, is too simplistic a model to capture the nature of the radio spectrum in local star forming galaxies. For example, Leroy et al. (2011) report a steepening beyond 4GHz of the spectral index for their sample of local starburst galaxies (i.e. U/LIRGs), and a flattening near 1GHz that they attribute to increasing optical depth effects at lower frequencies. A recent study of radio spectra in nearby normal star-forming galaxies finds evidence that the spectral index of the non-thermal component flattens with increasing SFR surface density (Tabatabaei et al. 2017). In addition, although broadly consistent with the standard M82 model, a significant variation in the contribution of the free-free emission to the total observed flux density is present in this sample.

The VLA-COSMOS 3 GHz Large Project data (Smolcic et al. 2017a), combined with the COSMOS multi-wavelength data-set (Smolcic et al. 2017b) provides strong evidence that the standard assumption of a typical radio SED for star-forming galaxies is inconsistent with what is typically found in deep surveys (already evident at moderate redshift, z>1; see Fig. 21 in Delhaize et al. 2017). The results suggest either a more complex shape of the typical radio SED for star forming galaxies, or the presence of an ensemble of radio SEDs representative of various types of star-forming galaxies (Molnar et al. 2018). These findings further imply that, when the application of a K-correction is needed, the regularly assumed simple, single-power-law shape (with spectral index of ~0.8) of the star-forming galaxy radio SED may easily lead to substantial systematic over- or under-estimation of radio luminosity. This becomes increasingly severe for high-redshift galaxies where significant corrections need to be applied to convert the observed flux density to the reference luminosity at 1.4GHz rest-frame frequency (so called K-corrections).

The proposed 6 & 10GHz imaging, together with the already existing 230MHz to 3GHz data, will allow us to measure the radio spectrum of (star-forming) galaxies out to z~2 and to determine the average spectrum of star-forming galaxy populations out to z~6. We will be able to check for the existence of spectral curvature across a broad redshift range, and how it evolves as a function of radio luminosity, SFR (from IR measurements), and other host properties (e.g. morphology) and redshift (see Tisanić et al. 2018 for a proof of concept). Furthermore, we will separate the radio continuum into its thermal and non-thermal component following the methodology of, e.g., Tabatabaei et al. (2017) and investigate the variation and dispersion in non-thermal contribution and spectral index as a function of galaxy properties and redshift. This work will provide the urgently needed insight into systematic biases and required corrections when using monochromatic radio continuum flux density. For the first time we will be able to derive the radio-SFR calibration over cosmic time.

Considerations for Achieving Main Science Goal

Calibrating the radio continuum as a SFR tracer out to the very young universe requires a deep field that is optimized for sampling the star-forming galaxy population out to the highest possible redshifts. Observations and theory/simulations show that most stars at all redshifts accessible (i.e. out to z~6) are born in galaxies with stellar masses of log(M*)~10-11 (e.g. Karim et al. 2011). The 2sq.deg. COSMOS field is therefore ideal, as all its observations are geared for this type of galaxies, especially with its deep near-IR imaging from Spitzer/SPLASH and VISTA/UltraVISTA (e.g. Laigle et al. 2016). COSMOS data ensure a statistically sound number of this important galaxy population that cannot be probed by optical (rest-frame UV) data. COSMOS is the only deep field with existing superb radio frequency coverage up to 3GHz. Thus we expect that most of the radio sources detected at 6 & 10GHz are detected at least at two other lower frequencies providing a good handle on their radio spectrum shape. Furthermore, the excellent ancillary data (including spectroscopic information for >60,000 galaxies out to z~7) allows us to robustly derive a multitude of host properties (e.g., M*, SFR).

The proposed project will return average radio continuum properties down to the very low-mass end (M*> 3e9Ms) sampled by the latest panchromatic COSMOS auxiliary data out to z~6. This will yield for the first time a virtually stellar mass-complete constraint on the cosmic star formation history from thermal radio emission at z<6. Our survey sensitivity is sufficient to provide for the first time constraints on the dispersion of the main sequence at masses well below the characteristic mass of star formation (logM*=10.6) across most of the universe's age (Karim et al. 2011).

The proposed observations, in conjunction with the panchromatic COSMOS database, will allow us to constrain the average radio SED of star-forming galaxies across cosmic time, and divided as a function of various galaxy population parameters, such as redshift, SFR, stellar mass, and magnetic field, and to calibrate radio continuum emission as a SFR tracer through cosmic time using i) independently from the (F)IR-radio correlation (see e.g., eqs. 11, 14, and 15 in Murphy et al. 2011), and ii) via the (F)IR-radio correlation derived using proper K-corrections, and thus eliminating systematics, biasing the results of current studies. Reaching the main science goal is paramount to facilitate star-formation studies within the planned projects with the SKA, ngVLA and their precursors.

The proposed 6 & 10GHz observations are key as they will allow us to probe the rest-frame frequency range up to 40-70GHz, i.e., the regime expected to be dominated by free-free emission arising from young star formation sites, at 3<z<6. Observations at both frequencies are crucial to achieve this goal as, combined with the COSMOS radio data, they allow for a full, continuous spectral coverage.

Time estimate

We propose to target the inner 1.8sq.deg (rms~2.8 and 2 uJy/beam at an angular resolution of 1.5’’, and 3’’ at C- and X-band, respectively) that has the best multi-wavelength coverage. We will cover the same contiguous area at 6 & 10GHz to allow for robust stacking experiments providing a stellar mass-complete constraint on the cosmic star formation history from thermal radio emission at z<6 as well as the dispersion of the main sequence. The target depths are set to detect ~50% of the 3GHz sources, yielding an expected number of ~2100 galaxies (z<6) detected at 6 & 10GHz. Note that most of the sources will have a detection also at 1.4GHz. Our predictions of detection rates are based on our independent estimate of the total star formation (see Delvecchio et al. 2017).

Assuming a hexagonal pointing layout we require for our 6 (10) GHz observations 524 (1486) pointings and ~39.9 (52.7) min observing time per pointing to reach a uniform rms over the field (with 25-27 antennas, and an effective 3.4GHz bandwidth). We request observations in D & B (6GHz), and D & C configurations (10GHz) resulting in resolutions of ~1.5"" (6GHz), and 3"" (10GHz), where the D configuration observations will comprise ~20% of the total requested time (to account for emission on large scales). Assuming the standard ~26% of overhead time, we thus ask for a total of 2090h of VLA time in B, C and D configurations (440h in C-band and 1650 in X-band). The brightest source in the 20 cm map is 23.5 mJy, thus dynamic range is not expected to be a limitation for imaging. We are working with the VLITE team to access and also use the commensal observations in P-band with our program.

COSMOS' (VLA) Radio Legacy

Across the radio band, and compared to other deep fields (e.g., ECDFS, Lockman hole) the COSMOS field already has the best coverage from 230MHz to 3GHz frequency, it has already been observed by LOFAR and it is a target field for MeerKAT and ASKAP key science projects (MIGHTEE, EMU). Additional single VLA pointing observations exist at 1.4GHz (CHILES, rms~4.2uJy/b, FoV~30', PI van Gorkom), 3GHz and 10GHz (rms~0.55 and 0.38uJy/b, FoV~15' and ~4.2', PI Hodge). VLBA-COSMOS observations toward all 1.4 GHz sources are available (Herrera-Ruiz et al. 2017), and about 10x deeper EVN-eMERLIN observations over a small area are approved (PI Radcliffe). Thus, the COSMOS field is one of the highest priority targets for radio observations with current and next generation facilities. In particular, the 1.4GHz VLA-COSMOS survey (Schinnerer et al. 2004, 2007, 2010) contributed to major advances in the studies of the dust-unbiased star-formation of galaxies (e.g. Carilli et al. 2008; Smolcic et al. 2009a, 2011; Schinnerer et al. 2008; Panella et al. 2010; Karim et al. 2011) and radio AGN, and their evolution through cosmic history (e.g. Smolcic et al., 2007, 2009b, 2015; Oklopcic et al. 2010; Jelic et al., 2012; Novak et al. 2015).

Since the first 1.4GHz catalog release in 2007 to date ~40 refereed publications including those from the community, with >1000 citations, arose from this data set. The 3 GHz observations conducted with the upgraded VLA (VLA-COSMOS 3GHz Large Project; rms=2.3uJy/b over 2sq.deg., 10830 sources with >5sigma; Smolcic et al. 2017a) provide to-date simultaneously the largest and deepest radio continuum survey at sub-arcsecond (0.75"") angular resolution, bridging the gap between last-generation and next-generation surveys. The first data and science release consisted of six publications, published as a special A&A issue, and it already provides the basis for more than ten published papers (Novak et al. 2015, 2017; Miettinen et al. 2015, 2017; Smolcic et al. 2015b, 2017a,b,c; Delvecchio et al. 2017; Delhaize et al. 2017, Molnar et al. 2018; Hale et al. 2018), and various papers in preparation, mostly led by PhD students (Ceraj et al., Tisanic et al., Leslie et al., Bondi et al., Vardoulaki et al., Jiménez-Andrade et. al.). The release was accompanied with a multi-country press release (see e.g. cosmos.astro.caltech.edu/news/52) that, internationally combined, received tens of thousands of hits.","We plan to continue our collaboration with the Observatory, noting that our team has all resources available needed for data reduction, analysis, and (data and science) release.

Data reduction and release plan

The VLA-COSMOS team is a team of radio-astronomy experts with extensive experience with VLA data, as well as AIPS, and CASA. This project will be co-lead by the three leads of the overall COSMOS collaboration, V. Smolcic (the PI of the 3GHz Large Project), C. Casey and J. Kartaltepe. The team will be fully dedicated to assure a high-quality and timely VLA data reduction and release (as we have already done with the VLA-COSMOS 1.4 and 3GHz surveys). Space to store the raw data (~60 TB expected) is already available at MPIA, AIfA (Germany), and University of Zagreb (Croatia). Following the COSMOS policy, robustly tested and verified catalogs of sources detected at 6 & 10GHz, as well as their radio- and multi-wavelength counterparts from the COSMOS database will be generated and released to the public in a timely manner (via the COSMOS IPAC/IRSA archive; see, e.g., the VLA-COSMOS 3GHz Large Project first data release paper series; www.aanda.org/component/toc/?task=topic&id=752). Two graduate students are already employed to work and benefit from the data-set, and more students will be employed to spend the majority of their time working on this data, starting with the data acquisition. Once catalogs are ready we expect that additional PhD students within the wider COSMOS team will base their theses on VLA-COSMOS 6 & 10GHz data (as was the case for the VLA-COSMOS 1.4 and 3GHz projects).

Next generation radio data catalogs

Main science goal: Calibrating radio continuum as a star formation tracer over cosmic time

To establish radio continuum emission as a robust SFR tracer out to the highest redshifts (into the epoch of reionization), we need to understand on a fundamental level:

A/ What is the shape of the galaxy-integrated radio spectrum and how does it evolve with cosmic time and radio luminosity for a given galaxy population?

B/ What is the relation between radio continuum and star formation powered (far-IR) emission and how does it evolve with cosmic time as a function of galaxy population?

Radio Spectral Energy Distribution (SED) & SFR Calibration

Considerations for Achieving Main Science Goal

Time estimate

COSMOS' (VLA) Radio Legacy

Data reduction and release plan

Next generation radio data catalogs

We are currently developing tools for automatic processing of radio data to automatically identify sources (including automatic association of optical counterparts), combine corresponding radio ""blobs"" into single sources, and also perform classification based on their radio morphology. This algorithm will be applied directly to the proposed observations to provide next generation radio catalogs, and thus will require a minimum amount of human intervention and visual inspection methods.",In order to push our understanding on the applicability of radio continuum as a star formation tracer to the next level that is mandatory for the proper exploitation of data from the next generation of major radio telescopes as the ngVLA a dedicated effort is required. The large time investment as well as the significant legacy value make this project very well suited for the eXtra-Large Proposal category.
COLDz-X: The Cold Gas History of the Universe,riechers@cornell.edu,D. Riechers (Cornell),"M. Aravena (Diego Portales), P. Capak (SSC/Caltech), C. Carilli (NRAO), R. Decarli (INAF), J. Hodge (Leiden), N. Scoville (Caltech), F. Walter (MPIA, NRAO)",4500,0,0,"We propose to carry out a measurement of unprecedented precision of
the cold gas history of the universe, i.e., the volume density of
molecular gas in galaxies as a function of redshift. Our recent VLA
Large Program COLDz used 324hr of Ka-band observations to demonstrate
that such a measurement is indeed possible, but due to limited source
statistics in the 375,000 Mpc3 volume probed by our initial survey,
the uncertainties attached to the measurement remain considerable. The
proposed ~15-fold expansion of the survey uniquely enabled by an
X-program will be required to obtain almost complete redshift coverage
over the entire z=1.5-7 range over a 3-11 times larger volume to
typically 3-15 times greater depths than COLDz, yielding an expected
improvement in the number of cold molecular gas detections by more
than an order of magnitude. This effort will be critical to pave the
way for the deep square degree scale large-area surveys that will only
become possible with the ngVLA over a decade from now.","The main goal of this program is the far most precise measurement of
the cosmic density of cold molecular gas in galaxies beyond redshift
1.5, with the byproduct of the far largest catalog of ""normal"", CO 1-0
selected galaxies and faint radio continuum emitters at a wavelength
sensitive to free-free emission in key extragalactic legacy fields to
be exploited by multi-wavelength studies of galaxy evolution by the
entire community. This survey will build on our successful large
programs at the VLA (COLDz; 324hr; Pavesi et al. 2018; Riechers et
al. 2018) and ALMA (ASPECS; 190hr), which demonstrate the feasibility
of these challenging measurements. Using the full 8GHz bandwidth of
the VLA, we will blindly select galaxies at redshifts z=1.4-2.7 and
3.8-6.4 through their emission in the CO 1-0 and/or CO 2-1 lines,
which are redshifted to the 31-39GHz (Ka band) and 40-48GHz (Q band)
ranges. These frequency ranges are chosen to optimize redshift
coverage and expected detection rates. As a pure detection project,
all observations need to be carried out in the D array configuration
to maximize point source sensitivity. As demonstrated by COLDz, a
wedding-cake-like survey strategy is optimal to provide the best
constraints on the CO luminosity function at high redshift. The
integral over the CO luminosity function then provides the total
cosmic cold gas density measurement at a given redshift. Critically
informed by COLDz and ASPECS, we will observe a single, ""ultra-deep""
1.3arcmin2 pointing to 5 times the depth of the current deep area of
COLDz (750hr in Ka band including overheads), to measure the faint end
of the CO luminosity function at high redshift down to values of
several times 10^8 K km/s pc2 for the first time. We will further
observe a ""wide-field"" area of 100arcmin2 to the depth of the current
(9arcmin2 in Ka band) ""deep"" tier of the COLDz survey (3750hr in Ka
and Q band). The resulting more than a factor of 20 increase in volume
in this tier is required to significantly improve the Poisson
statistics on the measurements of the CO luminosity function around
its knee and on the bright end. While COLDz covered a second,
51arcmin2 wide field, only 184hr were spent on this tier. As such,
this part of the survey was critical to measure the bright end of the
CO luminosity function, but it was not sufficiently sensitive to reach
the bulk of the gas-rich galaxy population. On the other hand, the
deep tier offered sufficient sensitivity, but the area was not
sufficiently large to achieve the required detection statistics for a
precision measurement of the cold gas history. COLDz-X, the proposed
extension of the survey through an X-program, will reach 5-15 times
deeper in the ""ultra-deep"" pointing and 3-5 times deeper in the ""wide
field"" survey component than the current COLDz reference survey, and
it will significantly enhance its redshift coverage (by a factor of 2
in cosmic time) and survey volume (to about 1,200,000Mpc3). COLDz-X
thus is the only way to substantially improve our knowledge of this
cosmologically important quantity until at least the late 2020s. This
survey will be a key pathfinder for ngVLA extragalactic legacy
surveys. The ngVLA will be the only facility to enable comparable
measurements on square degree scales, making it one of its priority
science goals already selected by the community (see ngVLA Science
Book).","1) Data analysis infrastructure for the duration of the
project. Estimated data volume required throughout the processing
period: 2,000TB. A minimum of 16-32 cores available, with a minimum of
128-256 GB of memory. Space required for long-term hosting of data
products (500 GB).

2) Personnel: One postdoc at the observatory for the duration of the
project to assist with setup of observations, managing incoming data,
and data analysis, as well as writing of publications.","Project will require an adjustment of the configuration schedule to be
completed within a reasonable time period (3-5 years), given the
requirement of the most compact configuration during high frequency
season (winter/spring). Project will likely require scheduling at
least of order 1000-1500 executions. Based on past experience with
large programs with at least somewhat comparable parameters (e.g.,
COLDz, CHILES), complete implementation and rapid completion of such
efforts are challenging without extending the parameters of the
current mechanism."
High dynamic-range observations of a mass-selected sample of galaxy clusters,ptozzi@arcetri.astro.it,Paolo Tozzi INAF (Italy),"Annalisa Bonafede (coPI) Bologna University & INAF (Italy)
Rossella Cassano (coPI) INAF (Italy)
Tracy Clarke (coPI) NAVY Naval Research Laboratory (US)
Simona Giacintucci(coPI) NAVY Naval Research Laboratory (US)
Reinout van Weeren(coPI) Leiden University (NL)
Monique Arnaud CEA Saclay Service d'Astrophysique (France)
Marcus Brueggen Hamburg University (Germany)
Gianfranco Brunetti INAF (Italy)
Virginia Cuciti INAF (Italy)
Daniele Dallacasa Bologna University & INAF (Italy)
Francesco de Gasperin Hamburg University (Germany)
Klaus Dolag Munich University (Germany)
Dominique Eckert Max-Planck-Institute for Extraterrestrial physics (Germany)
Stefano Ettori INAF (Italy)
Bill Forman Harvard-Smithsonian Center for Astrophysics (US)
Matthias Hoeft Tautenburg Observatory (Germany)
Massimo Gaspari Princeton University (US)
Fabio Gastaldello INAF (Italy)
Myriam Gitti Bologna University & INAF (Italy)
Melanie Johnston-Hollitt Curtin University (Australia)
Tom Jones University of Minnesota (US)
Francesca Loi Bologna University & INAF (Italy)
Gabriel W. Pratt CEA Saclay Service d'Astrophysique (France)
Piero Rosati University of Ferrara (Italy)
Mariachiara Rossetti INAF (Italy)
Huub Rottgering Leiden University (NL)
Larry Rudnick University of Minnesota (US)
Jack Sayers Caltech University (US)
Mauro Sereno INAF (Italy)
Tim Shimwell ASTRON (NL)
Franco Vazza Bologna University & INAF (Italy)
Tiziana Venturi INAF (Italy)
Denis Wittor Bologna University & INAF (Italy)
Heng Yu Beijing Normal University (China)
Irina Zhuravleva Stanford University (US)",1200,0,0,"Galaxy clusters are ideal laboratories for a variety of interconnected physical phenomena, from plasma processes and magnetic field amplification on large scales down to star formation processes and AGN feedback on small scales. Nuclear activity and star formation in member galaxies are best studied at high resolution, while the impact of these processes in the cluster environment needs observations sensitive to the large-scale emission. These processes are linked to the dynamical state as traced by the spectacular emission of radio halos and relics associated with major mergers. Moreover, such phenomena can only be understood with spectral information and polarisation measurements probing the magnetic field. Therefore, we propose an unprecedented, systematic investigation of a cluster sample with a interval in mass and z, consisting of an L-band, multi-configuration follow up of the XMM-Heritage sources. This mass-selected sample benefits from a unique, deep and uniform X-ray coverage, simultaneous 330 MHz VLITE data, extensive follow-up in optical/NIR, and LOFAR data that will optimally complement the JVLA data, enabling a wide range of diverse scientific goals.","Galaxy clusters are massive (Mvir ~10^14-15 Msun), gravitationally bound systems where dark matter dominates the total mass and coexists with hundreds of galaxies. About 15% of their mass is in the form of a rarefied (n~10^-3 cm^-3), hot (T~107 -8 K) gas (Intra-cluster Medium, ICM) that emits in the X-rays through thermal bremsstrahlung. In addition, radio data show synchrotron emission on a Mpc scale, revealing magnetic fields and ultra-relativistic electrons spread over the cluster volume. This requires that relativistic electrons are continuously injected or accelerated in situ, otherwise radiative losses due to synchrotron and inverse Compton would suppress the emission beyond of a few kiloparsec. Recent results show that the radio emission from cluster galaxies could have a key role in seeding relativistic electrons in the ICM. Moreover, the radio emission from the central AGN is also expected to significantly affect the thermal properties of the gas in the core, and to regulate the thermodynamics of the ICM via buoyantly raising bubbles inflated by radio lobes and shocks driven by the AGN activity.
Despite decades of study, we currently lack solid theories for the origin of the diffuse radio emission. Theoretical models make predictions that can be tested only through large statistical samples of clusters with known mass and dynamical status, and for which constraints on the magnetic fields can be obtained. Hence, to understand the connection between the activity of the member galaxies and the non-thermal components and to quantify the non-thermal pressure of the ICM, radio observations of a well-defined sample of clusters with known thermal properties are mandatory. Current studies are strongly limited by the low number of objects that can be requested with standard proposals, and by lack of a uniform radio and X-ray coverage, which are critical to avoid significant biases.
Here, we propose L-band, multi-configuration observations of a sample of galaxy clusters that has just been awarded 3000 ks of XMM-Newton time: the XMM-Heritage program ""Witnessing the culmination of structure formation in the Universe"" (PI M. Arnaud & S. Ettori). The XMM-Heritage cluster sample is SZ selected, which implies a robust selection in mass, allowing us explore clusters in several mass bins with high completeness. The target list is divided into two sub samples: a local (z<0.2, 10^14M⨀<M500<9⋅10^14M⨀) and a massive one (M500>7⋅10^14M⨀, z<0.6) that together will permit us to trace the evolution of the cluster properties with mass and cosmic time. The XMM-heritage sample consists of 118 clusters; 79 of them will be easily observable with the JVLA (-15°< DEC < 75°), and are the subject of this proposal.
The JVLA Extra-Large program we propose consists of a uniform coverage of these clusters in L band with multi-configurations, to reach sensitivity of ~5, 7, 16, and 30 μJy of rms per beam in the A, B C and D config, modeled on the experience with the Frontier Fields JVLA observation (see van Weeren et al. 2017, ApJ,835,197). This corresponds to ~3h in D array, 4h in C, B, and A array per cluster, for a total of ~1200 hours (exposure time on each target will be adjusted according to z). Targeting this sample would permit for the first time an unbiased comparison between the thermal and non thermal components both in the core and in the cluster outskirts, thanks to the uniform quality of the X-ray and JVLA data. At the same time, we will be able to constrain the magnetic field properties with polarisation observations. All JVLA data will also include simultaneous data from the 330 MHz receivers through the VLA Low-band Ionosphere and Transient Experiment (VLITE) back end. It is also important to note that 85% of the clusters observable by the JVLA will be observed by the Low Frequency ARray (LOFAR) Two-meter Sky Survey. The synergies between LOFAR, VLITE and the JVLA will permit a big step forward in our understanding of the diffuse radio emission in the ICM.
Such a program will provide a quantum leap for cluster science, and an invaluable heritage for the entire extragalactic community, thanks to the combination of statistics and high data quality of the XMM-Heritage with the high-dynamic range of deep, multi-configuration JVLA data. We detail below the scientific goals that we plan to achieve.
Nuclear activity & star formation
High-resolution imaging of groups and clusters of galaxies reveals the nuclear activity in the member galaxies as well as the star formation (SF) processes. L-band, high angular resolution data are thus key to trace the role of group and cluster environment in triggering accretion onto supermassive black holes (SMBH), or cooling of gas feeding SF. In particular, the brightest cluster galaxies (BCG) are known to have a key role in regulating the thermodynamics of the surrounding ICM. A detailed census of their nuclear activity complemented by the X-ray spectral analysis of the ICM would give insights into the feedback mechanisms. By correlating the ICM properties and the presence of radio AGN, we will be able test current accretion theories, such as chaotic cold accretion versus hot Bondi models (Gaspari et al. 2017, MNRAS,466,677) and to probe the infall of the cold gas clouds within the SMBH influence region as done in recent groundbreaking radio studies (David et al. 2014, ApJ,792,94, Tremblay et al. 2016 Natur,534,218; 2018, arXiv180800473). We also expect to detect the environmental effect of the dynamical state of the cluster by tracing the SF and nuclear activity as a function of the distance from the cluster center. For example, radio jets and lobes associated with FRI-like galaxies within clusters can be traced from the outer to the inner regions to an unprecedented level of detail and statistics.
A similar study, but on a much smaller scale and with a single configuration has been recently completed by our group (Yu et al. 2018, ApJ,853,100) where some of the CLASH clusters were observed with the JVLA in A config, L-band. We found that a systematic investigation of the BCG nuclear power allows one to establish a link with the presence of cavities in the ICM, star formation in and around the BCG, and the entropy of the surrounding ICM, providing several missing pieces to build up a comprehensive description of the cycle of baryons in the center of massive clusters. In addition, extrapolating from our experience, we expect to identify, thanks to the optical/NIR follow-up, about 1400 cluster members across the entire sample, allowing a systematic study of nuclear and SF activity in the galaxy population.
Particle re-acceleration processes in the ICM
Radio halos are synchrotron sources extending on Mpc scale in central regions. A connection between cluster dynamics and presence of radio halos has been established, with radio halos preferentially found in mergers (Cassano et al. 2010, ApJ,721,82). The gravitational energy dissipated during the hierarchical sequence of mergers that generate diffuse turbulence, could re-accelerate pre-existing electrons in the ICM to the energies necessary to produce the observed radio emission (Brunetti & Jones 2015, ASSL,407,557). Therefore, it is key to study the correlations between the amplitude of ICM density/temperature fluctuations and the radio power by leveraging the Fourier analysis (Gaspari & Churazov 2013, A&A,559,78).
According to turbulence acceleration models, the formation history of radio halos depends on the cluster merging rate throughout cosmic epochs and on the mass of the host, which sets the energy budget available for particle acceleration. Radio halos should be preferentially found in massive objects undergoing energetic merging events, while they should be less common, and showing steeper spectra, in less massive systems. Hence, radio halos would become under luminous at higher frequencies (Cassano et al. 2010, A&A,509,68). A recent exploratory study (Eckert et al. 2017, ApJ,843,29) has shown that giant radio halos follow the turbulent scaling (P1.4GHz~ σv3), corroborating the importance of linking the X-ray thermodynamical properties of the ICM with the radio observables.
So far, statistical studies of clusters in radio have been limited to very massive systems, (M500 > 6 10^14 M⨀) which are the rarest in the Universe. Hence, we are likely observing the tip of the iceberg of the population of radio halos, while many of them could be discovered at low mass. The Heritage-XMM sample is ideal for such a study because of its wide mass range. In addition, the combination of LOFAR, VLITE and JVLA observations will enable us to determine the spectral indices of radio halos, and constrain the occurrence of radio halos at high and low frequency. X-ray data with a large FOV are fundamental as they permit us to investigate a link between cluster dynamics and radio emission.
Radio relics are elongated Mpc-size sources located in the outskirts of galaxy clusters, possibly associated with shock fronts, where particles are being (re-)accelerated. The key observational facts that support the shock-radio relic connection are (i) the high polarization, with the magnetic field vectors parallel to the major axis of the relics, indicating that the ICM and magnetic fields are probably compressed, (ii) the presence of spectral index gradients, indicating electron cooling in the post-shock region of an outward traveling shock wave, and (iii) the presence of ICM density and/or temperature jumps at the location of several relics (van Weeren et al. 2010 Sci,330,347).
Although the above observations support the basic scenario, there are still several important open questions and observational puzzles. X-ray observations indicate that the shock Mach numbers corresponding to relics are low, typically ≲3. Based on the diffusive shock acceleration (DSA) model, this implies a poor efficiency of acceleration at such weak shocks. A possible solution is that the shock re-accelerates a population of already mildly relativistic electrons, instead of directly accelerating them from the thermal pool (Kang et al. 2012, ApJ,745, 146). There is some observational support for this shock re-acceleration model, where old fossil electron from radio galaxies are revived at shocks (van Weeren et al. 2017, NatAs,1,5). However, we lack the statistics to test this hypothesis. Another unsolved issue concerns the filamentary morphology of relics as recently revealed in few deep JVLA observations (Owen et al. 2014, ApJ,794,24). Are these filaments tracing the tangled ICM magnetic field, or do they reflect the complex nature of the shock surfaces? To answer these questions, it is fundamental to have a large sample of radio relics with radio and X-ray observations, observed in mass(SZ)-selected clusters at different mass and z. X-ray data can constrain the shock properties, and radio observations will enable us to constrain the magnetic field (through polarisation observations) and the connection with the AGN.
Radio minihalos are diffuse, synchrotron-emitting sources located in the cool core of galaxy clusters. They are often bounded by one or two X-ray cold fronts, which are sharp surface brightness discontinuities in the X-ray images, with the denser region colder than the more rarefied one. Cold fronts are believed to originate from sloshing of the cool core gas in the deep potential well in response to a minor merger, or to a powerful AGN explosion in the BCG (Markevitch & Vikhlinin 2007, PhR,443,1). Sloshing motions could trigger turbulence in the cool core, and accelerate a seed population of relativistic particles producing diffuse radio emission. Alternatively, minihalos could originate from hadronic collisions of cosmic-ray protons with the thermal protons in the ICM (see Brunetti & Jones 2015, ASSL, 407).
Recently, Giacintucci et al. (2017, ApJ,841,71) investigated the occurrence of minihalos in a statistical sample of massive clusters (M500 > 6 10^14 M⨀) showing that minihalos are only found in cool-core clusters, and that 80% of cool cores in their sample host a minihalo. However, the connection with sloshing cold fronts and cluster mass needs to be further investigated with a rigorously mass-selected, large sample of clusters, observed with a uniform X-ray and radio sensitivity, and covering a wide range of cluster masses. A follow-up of our sample would permit us to: 1) constrain the occurrence of minihalos as a function of cluster mass; 2) understand the connection between minihalos and cold fronts; 3) in combination with LOFAR survey data and VLITE, derive the spectrum of the radio-emitting particles, which encodes information on the physical origin of minihalos. Having combined information on the cluster magnetic fields in mass bins and on the radio spectrum will permit us, for the first time, to derive the particle energy distribution.
Polarization studies and magnetic fields
The knowledge of magnetic fields in galaxy clusters is of paramount importance to understand the non-thermal energetic budget, the particle acceleration mechanisms, and any other plasma processes at play in the ICM. AGN feedback and thermal conduction also depend of the magnetic field properties. A key information is provided by Faraday Rotation measurements (RM) of polarized sources inside or in the background of clusters. So far, such study has been carried out on a few clusters (e.g. Coma, Bonafede et al. 2010, A&A,513,30), as there are not enough sources available for individual clusters. Therefore, the only way to address this issue is statistically, with a large cluster sample. The Jansky VLA is the only instruments that is currently able to carry out a project like this, and the XMM-Heritage clusters represent the ideal sample for this study, as it will yield a precise and unbiased description of the gas density distribution, which is mandatory for this analysis.
Assuming a typical polarisation fraction of 5%, the proposed observations will allow us to detect ~1600 sources in polarisation in the background (1 Mpc2 area), at 3σ (Rudnick & Owen 2014, ApJ,785,45). This would permit: 1) constraints on the magnetic field properties; 2) the detection of enough sources at different distance from the centre to constrain, for the first time, the universal magnetic field profile; 3) to trace the magnetic field with cluster mass. In addition, a substantial number of background radio sources will be detected outside clusters, yet in the region where the beam-squint effect is negligible. These sources will serve as control sample as they are unaffected by the cluster properties. Numerical simulations (see Bonafede et al 2013, MNRAS,433,3208) will be used to constrain the magnetic field from observations. This will be the largest sample of RM detected through clusters, and will remain such until the next generation of radio instruments will be operative.",No special resources are required.,"Only an XLP can cover all the Heritage clusters visible from the JVLA with the required depth and range of angular resolution, actually enabling all the mentioned science cases. The total estimated time we need to reach the scientific objectives is ~ 1200 hours, considering multi-configuration L band observations for all the clusters in the sample. The largest configurations will permit us to study the nuclear regions, the galaxy population, and derive Faraday Rotation Measure information avoiding beam depolarisation, while the most compact configurations will be needed to maximise the sensitivity to the extended emission. All observations will have simultaneous 330 MHz VLITE data to add to the JVLA legacy.
The strength of this proposal is that we will have a large sample of clusters with uniform X-ray and radio sensitivity, that will provide a unique deep and multi-scale view of the processes at play in the ICM. Feedback from central galaxies, shock and turbulence acceleration, as well as studies of the magnetic fields from the Faraday effect are deeply connected with the characterization of the ICM thermal properties, provided by X-ray observations.
The observations from this project will have a huge scientific impact on the cluster community, and an important legacy value. However, these observations will also be useful for a broader range of astrophysical fields than the cluster community. Magnetic fields play an essential role in thermal conduction and are responsible for several plasma micro instabilities (Schekochihin et al. 2005, ApJ,629,139); magnetic fields affect the evolution of galaxies, by mediating the interaction between galaxies and the medium, and affect the propagation of the very high energy cosmic rays. Moreover, magnetic fields and ultra-relativistic electrons may affect the cluster mass estimates by providing an additional term of pressure support. In the coming era of precision cosmology, this contribution must be considered to derive constraints on the cosmological parameters down to the percent level. Systematic studies of AGN and SF occurring in member galaxies will greatly benefit from a high-resolution imaging in the L-band, helping to quantify the triggering mechanism as a function of the virial mass and dynamical status. The comparison of ICM properties from X-ray with the feedback associated to the BCG and other galaxies can track the baryon cycle in the central regions of clusters, unveiling complex phenomena which are at the core of galaxy formation and evolution.
To summarize, the high-statistics and high-quality data of the XMM-Heritage sample build upon a rigorous SZ selection equivalent to a mass selection, combined with a high-dynamic range coverage in the L band with JVLA (and simultaneous VLITE data), will have a profound impact on the cluster community at large."
Understanding the Known Pulsar Population,Evan.Keane@gmail.com,Dr. Evan Francis Keane,Dr. Cristobal Espinoza,0,3000,0,"How radio pulsars work is still an unsolved problem over 50 years after their discovery. Investigations of how pulsars work are usually over-shadowed by studies that simply use pulsars as tools (typically as high-precision clocks) to investigate other astrophysical questions. Most of the 2546 radio pulsars known [1] are rarely, or never, observed. The process by which new discoveries are triaged is flawed and subject to bias. It is common to quickly identify possible Pulsar Timing Array sources (i.e. the very best clocks), as well as those in few-hour (i.e. highly relativistic) binaries, and to ignore the rest. An X Proposal using the GBT that focuses on the known population would change this, and yield a wealth of fundamental information on pulsar properties. The predictable outcomes include the intermittency and nulling distributions, their prevalence, time-scales and magnitudes; pulsar glitch properties especially those of the smallest events and identification of glitch quanta (and hence superfluid interior physics); time evolution and braking behaviour of the spin characteristics (and hence the slow-down mechanisms), pulsar spectra (and hence emission and environment physics).","
This expression of interest for X Proposals looks to perform ~monthly observations of 200 already-known pulsars over the course of 3 years, amounting to 3000 hours of GBT time in total.

With a well-designed strategy, that takes specific properties into account to define each pulsar's ideal observing cadence, it would be possible to produce a long-term dataset that would allow the detection and tracking of phenomena occurring on timescales from days to months. After the three years the datasets would provide enough statistical value to accomplish solid and deep studies of these phenomena.

Most of the resources used to observe pulsars today are dedicated to monitoring millisecond pulsars that are part of the Pulsar Timing Arrays (PTAs); to use pulsars as precise clocks to study other astrophysical phenomena, and to find new pulsars. The vast majority of the known pulsars are not observed much beyond their discovery. However, after more than 50 years since their discovery and there still remain many unknowns in pulsar physics: we still do not understand how pulsars emit, what determines their slow down, or what are the properties of the matter in their interiors.

Some non-PTA pulsar monitoring has been undertaken over the last decade at Parkes for the sub-sample timed for the Fermi mission. Elsewhere, monitoring of hundreds of pulsars is undertaken, but at far lower S/N levels than GBT could achieve, at Jodrell Bank (for decades) and with the upgraded Molonglo system (since 2015). GBT’s capability, especially in L and S bands [2], is far superior to these studies; while Effelsberg is comparable, its declination range and the lack of any such legacy project opportunity, mean that it could not perform this work. The best direct comparison to GBT is MeerKAT, now in its latter commissioning stages. Its 1-km core is roughly equivalent in gain (both ~ 300 m^2/K) to that of the GBT at L-band [3]; survey speed is an irrelevant metric for a targeted project such as this. MeerKAT has one legacy programme (MeerTIME) with one sub-project (“1000-Pulsar Array”) with somewhat similar aims, but here we are advocating for a much deeper look at a smaller (but still large) number of pulsars.

Many effects that we will search for are subtle (e.g. profile changes associated with magnetospheric state changes [4], or looking for the quanta of pulsar glitches[5]) and so our strategy makes a unique and complementary addition to those undertaken elsewhere.

The plan would be to perform regular observations at two or more observing frequencies and record polarization information every time. With the high S/N achievable with the GBT, and in combination with an apropriate cadence for each pulsar, after a couple of years the dataset would allow deep and consistent studies of the emission mechanism and the majority of the transient phenomena known to populate pulsar observations. For instance:

- It would be possible to inspect the universality of the correlation between pulse shape variations and two or more spin-down regimes, which has been found in some pulsars [4]. With this it could be possible to make real progress towards understanding the physical origin of timing noise, which is one of the main rotational irregularities that affect the otherwise stable rotation of pulsars. Timing noise affects millisecond pulsars too, hence this is highly relevant to the use of PTAs to detect gravitational waves.

- The emission of pulsars is not constant and many pulsars exhibit nulls, or moments of non detectable emission, lasting several rotations. With the GBT it would be possible to study this in much more depth and, for instance, explore any possible connections between nulling and intermitent pulsars and the so-called Rotating Radio Transients (RRATs). The former are pulsars that exhibit much longer nulls (days to months), which have also been associated with different spin-down regimes. RRATs are pulsars that emmit detectable pulses only very occasioanlly and in many cases appear to be in an almost constant null state.

- Glitch studies, which are in direct connection to the interior dynamics of neutron stars, will also be benefited by this programme. Glitches are sudden spin up events in the rotation rate, thought to be produced by the interplay between the crust of the star and an internal neutron superfluid. While large glitches are hard to miss, the detection of the smallest events becomes highly compromised if the cadence and S/N of the observations are not appropriate. With this monitoring programme we could attempt to determine the lower end of the glitch size distribution [5]. Furthermore, with well-planned observations, post glitch effects can be characterized not only for the largest events (which is what currently happens) but for all of them.

- As well, the dataset would permit, among many other applications that we do not have a space to address in this EoI, the study of pulsars' spectra and its stability; the characterisation of the spin evolution of the youngest objects; and to determine properties of the interstellar medium in the direction of pulsars.

Finally, it cannot be ruled out that the final dataset would also allow the discovery of new phenomena. Pulsar science has a history of fundamental discoveries cropping up when care has been taken to look deeply at particular sources.

The use of pulsars as tools to study other astrophysical topics will eventualy require a deeper knowledge of neutron star physics as this will be the ultimate limiting factor in those studies - you must fully understand your tools to understand the measurements made with them. The volume of data, number of pulsars, accuracy of the measurements and cadence would make this a unique dataset to start filling this gap.

References Cited Above:
[1] PSRCAT version 1.58
[2] http://www.gb.nrao.edu/scienceDocs/GBTog.pdf
[3] https://ui.adsabs.harvard.edu/?#abs/2018IAUS..337..158K
[4] https://ui.adsabs.harvard.edu/?#abs/2010Sci...329..408L
[5] https://ui.adsabs.harvard.edu/?#abs/2014MNRAS.440.2755E/","In addition to standard pulsar observing backends and associated pipelines it would be beneficial to have help with the significant data storage need, and in the maintenance of several databases (to keep track of observations, diagnostics etc.) and web pages. We are happy to provide resources in this regard, or likewise to work with NRAO on this, as appropriate. Additional meta-data ,that may not be standard, but that we would need to access include site and telescope data, e.g. observing logs, RFI monitors and other QA data products. The data collected in this project will serve as a legacy dataset for many years to come so there is a long-term resource need in this regard. For our part we commit to fully providing and maintaining these to the community into the future, in collaboration with NRAO.","This project requires a large amount of dedicated time over many semesters that both exceed the scope outlined in the NRAO Large Proposal Policy. Thus such a project, as discussed here, could only be performed via something like an X Proposal"
A deep synoptic radio survey toward intermediate/high-mass protoclusters: search,busquet@ice.cat,"Gemma Busquet (ICE, CSIC-IEEC)","Josep Miquel Girart, Joao Alves, Nacho Añez-López, Crystal Brogan, Robert Estalella, Manuel Fernández-López, Jan Forbrich, Todd Hunter, Zhi-Yun Li, Daniel Lin, Hauyu Baobab Liu, Rosario López, Fanyi Meng, Karl M. Menten, Aina Palau, Adele L. Plunkett, Alvaro Sánchez-Monge, Patrick Sheehan, John Tobin, José Maria Torrelles, Qizhou Zhang",1500,0,0,"When and in what stage massive stars form relative to their low-mass cluster members is still an open question. The lack of an observational characterization is due to the large distances involved and the cluster nature, which call for high angular resolution and high sensitivity observations. The goal of this project is to obtain deep, large-scale radio continuum observations at several frequency bands toward a collection of intermediate/high-mass protoclusters located at distances <2 kpc with the JVLA in the A and B configurations. The strategy is to observe first a sample of protoclusters in Orion Molecular Cloud to generate a template of the YSOs population, from the extremely young Class 0 objects to the more evolved Class III YSOs. Using data at other wavelengths available in the literature, we will characterize the radio emission, the spectral index and variability, and investigate how they change as a function of luminosity and age. Having the Orion template, we will then extend the study and apply all this knowledge to a sample of 20 intermediate-/high-mass protoclusters. Simultaneous X-ray observations are planned to investigate the radio and X-ray variability.","Intermediate-/high-mass stars generally form in clusters accompanied by low-mass stars. Nonetheless, it is not known whether these populations form sequentially or contemporaneously. Moreover, it is interesting to probe the earliest stages at which ionization might be present to investigate the implications of stellar feedback that could soon disrupt the star-forming cores and limit their further growth. One challenge to better understand these formation scenarios is that high-mass star-forming regions are mostly distant and clustered, both factor requiring high resolution and sensitivity. By observing a collection of regions harboring intermediate-/high-mass stars, and with the sufficient sensitivity to also detect their associated low-mass neighbors, we aim to investigate the formation mechanisms in the cluster context.

Deep radio continuum surveys in nearby regions such as Ophiuchus or Perseus have shown the potential to characterize the population of Young Stellar Objects (YSOs) at radio wavelengths and their characteristics at other wavelengths (Dzib et al. 2013, Pech et al. 2016). The new capabilities of the JVLA offer now a unique opportunity to extend such detailed studies in nearby molecular clouds to more distant regions where massive stars form. Currently, only the Orion Nebula Cluster has been observed with high sensitivity and angular resolution to obtain a complete census of the YSOs population and their properties in the radio domain (Forbrich et al. 2016). The goal of this project is to obtain deep, large-scale radio continuum observations toward a sample of intermediate/high-mass protoclusters located at distances < 2 kpc.

The radio continuum emission at centimeter and millimeter wavelengths is found in association with young stellar objects (YSOs) tracing both radio jets and disks and in all the stages of star-formation process, from extremely young protostars (Class 0 objects) to pre-main sequence stars
(Class II/III objects). In the 5–30 GHz range the radio emission of low-/intermediate-mass YSOs arises from several mechanisms: i) thermal bremsstrahlung (spectral index between −0.1 and +2), interpreted as free-free emission from ionized, collimated gas tracing the base (the region closer to the origin) of the large-scale optical jets and molecular outflows; ii) non-thermal, either from very active stellar magnetospheres, typically found in Class II/III objects, or from shocked spots in the jet lobes located far from the central powering source, typically associated with a negative spectral index; iii) dust from protoplanetary disks, mainly tracing large grains (> 100 μm) and with a spectral index of dust 𝛼dust~2-3. These mechanisms have a characteristic spectral index, and thus it is necessary to observe the YSOs population covering a wide frequency range.

Regarding the radio continuum emission associated with massive stars, during the very first stages of their formation, the centimeter emission would be dominated by thermal radio jets with spectral indices around +0.6, but also with negative spectral indices associated with synchrotron emission coming from shocks in the jet. Once the star is radiating UV photons, the emission at centimeter wavelengths would arise from a photoionized jet (with a spectral index of +0.6 but with a larger flux) and from photoevaporated disks (with spectral indices between +0.6 and +2). The next stage would be dominated by the development of an hypercompact or ultracompact HII region, with spectral indices from +2 to -0.1, as the HII expands.

This project aims to obtain sensitive radio continuum observations (full polarization) at different frequencies (C, X, and K band observations) with the JVLA in the A and B configurations toward a sample of intermediate/high-mass protoclusters located at distances < 2 kpc and covering a range of luminosities. All the selected regions have been observed at other wavelengths (i.e., in the millimeter/submillimeter range using interferometers, at infrared wavelengths with Spitzer, X-rays, and even with the VLA but at low angular resolution and/or with low sensitivity). For example, to detect the YSOs population of Ophiuchus, typically with flux densities of ~1 mJy, we need to reach an rms for X-band observations of 1 microJy/beam for a 5 sigma detection in a region located at 2 kpc. In addition to the continuum emission, we also plan to include some spectral windows for line emission studies. In particular we will cover the CH3OH maser line at 6.7 GHz, the H2O maser line at 22.235 GHz, and some radio recombination lines.

The main goals of this project are:

1. To obtain a unique census of the stellar population in intermediate-/high-mass protoclusters that combined with data from the literature will help to constrain the evolutionary stage of the low-mass population.

2. To derive the spectral index from multifrequency observations to characterize the nature of the emission, specially to identify non-thermal emission with negative spectral index. This type of emission can arise either from background extragalactic sources or from relatively evolved (Class II/III) YSOs with an active magnetosphere.

3. To compare the radio properties of the YSOs with the characteristics obtained from previous detailed observations at other wavelengths (millimeter, infrared, and X-ray).

4. To look for variability of the detected radio sources. YSOs are known to exhibit strong radio variability, and even in some cases in the form of extreme radio flares at short timescales. Recent simultaneous X-ray and radio observations of the Orion Nebula Cluster (Forbrich et al. 2016, 2017) have for the first time shown in more detail how X-ray and radio flares are related, and significantly more data is now needed to explore further the resulting impact on protostellar environments. Such observations can be ideally combined with the above main science goals. Thus, the present project aims to conduct simultaneous X-ray Chandra and JVLA observations.

5. To investigate the spatial distribution of the cluster members and its relation with the evolutionary stage and mass, which can provide information on the coeval or delayed formation of massive stars with respect to low-mass stars.

The strategy to conduct the proposed JVLA eXtra Large Project is the following. First, we will observe several fields (~) of the Orion Molecular Cloud (OMC) encompassing deeply embedded protoclusters to generate a template of hundreds/thousands of YSOs, from Class 0 to Class III. It is worth noting that only the Orion Nebula Cluster, which is a fraction of the OMC, has already been observed with the JVLA (Forbrich et al. 2016). Our team already has reference imaging in the OMC region and in this project we will be extending to a representative set of protoclusters. Together with data available from the literature, from near-infrared to the millimeter range, we will characterize the radio emission, the spectral index and variability and look for how it changes as a function of luminosity and age. Then, all the knowledge that we can learn from the Orion protoclusters can be applied to more distant regions to identify and characterize the radio population. Therefore, besides the fields to be observed in OMC, we have selected a collection of 20 intermediate-/high-mass protoclusters located at distances < 2 kpc that will provide a unique legacy for protclusters studies in the centimeter range.","The project requires standard observations. However, it demands an extremely high volume of data storage and processing, hence disk space and CPU is an important factor. For example, a single execution for one region and in X-band only will be around 250 GB in raw data size. Thus, given that the project requires observations at different frequencies and towards a sample of star-forming regions, we would need some resources from NRAO for data storage as the raw data will easily exceed 50 TB. Our group can also provide additional support for data storage and processing, and a PhD student can also visit the NRAO for extended periods of time to manage the data.

In addition to the radio continuum and full polarization observations, we also plan to include the emission of maser and radio recombination lines in the setup. Reliable spectral line calibration in the pipeline will be critical for this project, and if it would be helpful, our team would be willing to supply testing effort in the early days of the project to ensure this goal is met.","The proposed project is better suited for an eXtra-Large Proposal mechanism because it requires observations at different epochs to study the variability of radio sources. The timescale for radio variability may vary from weeks to months. Therefore, given that such X-Proposals will be executed during several years it is better suited than a regular Large Proposal.

In addition, the project requires high-frequency observations (K band) with the most extended JVLA configuration. Hence, we will need more than one A-configuration cycle to observe the targets during night time and at high elevation, when the conditions are the best for high-frequency observations."
A panchromatic radio view of the star forming ISM in galaxies,e.brinks@herts.ac.uk,Elias Brinks,"Volker Heesen, George Heald, Adam Leroy, Eric Murphy, Jonathan Westcott",2100,95,0,"We propose an ambitious project to improve our understanding of the physics underpinning the “radio continuum - star formation rate"" (RC-SFR) relation and determine to what extent the non-thermal radio continuum can be calibrated to provide an extinction-free SF indicator. We will map the spatially resolved radio spectral energy distribution (SED) of 21 nearby, late-type galaxies from P-band up to Ka-band, at matched 2” - 4” angular resolution, using multiple VLA configurations. The GBT, offering matched frequency coverage, will be used to provide crucial short spacing observations. The higher frequency bands will be used to characterise the free-free contribution due to current star formation and any contribution by ‘spinning dust’. We will subsequently derive maps of the non-thermal emission only, map the spatially resolved SED, map and model cosmic ray propagation and spectral ageing, and link this to the characteristics and morphology of the magnetic field. Our aim is to understand which factors govern the RC-SFR relation as some of these may evolve with redshift and hence affect the interpretation of upcoming deep surveys with the VLA (VLASS) and SKA Precursors.","Introduction

Ionising UV radiation from massive stars creates HII regions where thermal electrons give rise to RC radiation through the process of Bremsstrahlung or thermal (free-free) emission. These same stars explode as core-collapse SNe (type Ibc and type II SNe). The supernova blast wave accelerates cosmic ray electrons (CRe) which, when they encounter a magnetic field generate non-thermal (synchrotron) emission. If all CRe lose their energy exclusively within the galaxy, it can be considered a calorimeter (Voelk 1989, Lisenfeld et al. 1996). More realistically, a galaxy is a leaky box, and models become far more involved, e.g., Bell (2003) and Lacki et al. (2010). The relative successes of theoretical models lend confidence to the notion that massive star formation and RC emission are closely tied together (e.g., Condon et al. 2002). As shown by Niklas & Beck (1997), a properly calibrated RC-SFR relation can be used to derive SFR density maps and, with observations of the gas phase (HI and H2) offer an alternative, and independent method to study the relation between gas density and star formation (Schmidt-Kennicutt relation; Kennicutt & Evans 2012). Our aim is to obtain a complete understanding of the physics governing the RC-SFR relation as some of the factors involved may evolve with redshift and hence affect the interpretation of deep surveys with the VLA (VLASS) and SKA Precursors, probing galaxy evolution and the Cosmic SFR across redshift (Murphy et al. 2009; Schleicher & Beck 2013), where the sub-Jy population of normal starforming galaxies are expected to dominate the number counts.

Although FIR emission in principle can provide an extinction-free measure of the SFR, deep FIR observations depend crucially on space-based observatories that provide at best modest angular resolution and are therefore limited by confusion; the radio continuum offers a powerful, high resolution, widely available, near extinction-free alternative. That is why we focus here on the RC-SFR relation entirely.

The Project

Thermal RC, which dominates the radio spectral energy distribution (SED) at frequencies higher than 10 GHz and has a flat frequency dependence (spectral index of -0.1), is expected to be directly proportional to the SFR, as both are in principle tracing the ionising flux from massive stars. First results from the Star Formation in Radio Survey (SFRS; Murphy et al. 2012) indeed seem to confirm this.

The non-thermal RC, which dominates at the lower frequencies and has a power-law spectral index with slope -0.5 to -1.0, depends on the magnetic field strength as well as the cosmic-ray energy density. Whereas the thermal emission is strictly coeval with a current SF event, non-thermal emission has a longer lifetime, depending on the electron energies (i.e., frequency at which the CRe radiate), the synchrotron SED gradually steepening as the higher energy CRe lose energy fastest. Usually one assumes energy equipartition between the CRe and the magnetic field, so that the RC-SFR relation is closely connected to a relation between the magnetic field and gas. For spatially resolved studies, the non-thermal RC-SFR relation is further affected by the effects of cosmic-ray transport, which smears out the distribution of the non-thermal RC with respect to that of the SF region.

Despite the non-thermal RC, which dominates at frequencies below 10 GHz, being the result of complex interactions between CRe and the ISM, it is potentially more attractive than the thermal RC due to its steeply rising spectral behaviour; flux densities increase by up to an order of magnitude over one decade in frequency whereas the noise and receiver characteristics across the band remain fairly flat. Also, at lower frequencies the instantaneous sky coverage is larger which makes deep, wide area, high redshift surveys vastly more efficient. A well understood and calibrated, non-thermal RC-SFR relation would be a powerful tool!

To address the above, we propose to:

- map 21 nearby (3.2 < D [Mpc] < 14.1) late-type galaxies at P-, L-, S-, C-, X-, Ku-, K-, and Ka-band, each across a range of VLA configurations to ensure matched angular resolution of 2” - 4”;
- use the GBT to make ‘on the fly’ (OTF) maps using the same frequency bands to measure the total flux and provide the short spacings that are missing in the VLA observations;
- derive total and polarised intensity maps and map the SED on a spatially resolved basis.

The PI and Co-Is have been preparing the way for the ambitious project proposed here. In the following we list the various work packages we foresee and describe the projects we have been involved in that have helped us to develop the tools to efficiently, effectively, and consistently analyse the data from the proposed observations.

WP1- The observations will result in a data cube for each target of flux density in RA and Dec with as the third dimension a fully, and densely sampled SED. We will use our Bayesian SED analysis (Westcott et al. 2018) on the data cube to derive on a beam by beam basis (i.e., 2” - 4” resolution) two new data cubes, one of the thermal and the other the non-thermal emission. It is important to stress this decomposition uses exclusively our radio data without the need for any further, usually optical data which would introduce considerable uncertainty because of extinction, notably on small linear scales. The cubes will be used to create thermal and non-thermal maps as well as a spectral index map and a map of the thermal fraction, the latter three at a chosen fiducial frequency, typically at 1 GHz. With the thermal and non-thermal contributions properly separated, one can synthesise a radio map at any frequency for either thermal or non--thermal contributions (between the upper and lower frequency limits) and test how redshift may affect the observations. Also, with the full frequency coverage as proposed, one can test which methods are available, and their uncertainty, to reliably separate the thermal contribution when dense SED sampling is not, but ancillary data is available.

WP2- The thermal data cube will substantially extend the Star Formation in Radio Survey (SFRS; Murphy et al. 2012). It will be used to ascertain to what degree the data can be used as a robust star formation rate (SFR) indicator and compare radio derived SFRs against other empirical calibrations such as those relying on different combinations of warm 24 μm dust, total infrared (IR; 8–1000 μm), Halpha line, and far-UV continuum emission. In addition, because the full SED up to 33 GHz is covered, it will be possible to identify any contribution by AME and, importantly, to isolate this spatially, shedding further light on this enigmatic contribution to the radio SED which was only discovered 20 years ago (see Dickinson et al. 2018, for a review). Lastly, we will use the thermal emission to predict the expected Halpha emission, the ratio of observed over predicted Halpha providing a measure of extinction variations in the targets, and the intrinsic extinction in HII regions (see Westcott et al. 2018, to see this applied to NGC 1569). This is one of the drivers for the angular resolution required.

WP3- The non-thermal map will be used to derive the spatially resolved RC-SFR relation at a chosen reference frequency, with as 2nd parameter the non-thermal spectral index. The SFR indicators will be based on the extensive work by Leroy et al. (2008, 2009, 2012). This WP builds on an analysis by Heesen et al. (2014) of the RC-SFR relation using the WSRT-SINGS 20-cm radio continuum survey (Braun et al. 2007, 2010). Heesen et al. (2014) find that they can reconcile the finding of an almost linear RC-SFR relation and sub-linear resolved (on 1kpc scales) RC-SFR density relation by proposing a non-linear magnetic field-SFR relation with a power law slope of 1.3, which holds both globally and locally. This is within the errors consistent with the results of Niklas & Beck (1997). If the magnetic field, as these authors propose, is regulated either by the star formation rate density or gas density, and there is a gas-SFR relation, the radio-SFR relation would be a natural consequence. The theoretical underpinning for this is provided by Schleicher & Beck (2013).

Hindson et al. (2018) extend this result to the realm of dIrr galaxies, analysing their 6-cm VLA survey of 40 galaxies taken from LITTLE THINGS (Hunter et al. 2012) They find an average thermal fraction of 50% - 70% and an average magnetic field strength of 5 - 8 muG, only slightly lower than that found in larger, spiral galaxies. Interestingly, at 100 pc scales, they find locally surprisingly high values of up to 50 muG.

WP4- The non-thermal data cube can be analysed further and radio SEDs can be extracted at any position for spectral index (model) fitting, e.g., using BRATS (Broadband Radio Astronomy ToolS; see for a description of the method Harwood et al. 2013). The above described approach builds on an earlier pilot project by Heesen et al. (2015) where they analysed the SED of the non-thermal superbubble in the nearby dwarf irregular galaxy IC10. We will investigate the non-thermal radio spectral energy distribution on a spatially resolved basis and relate its characteristics (curvature, CRe age, CRe injection spectrum) to the RC-SFR relation. On the low frequency side, the effects of absorption mechanisms, such as free-free absorption should become noticeable. As intimated by Chyzy et al. (2018), free-free absorption manifests itself on local scales (at that of the HII regions), again arguing for the angular resolution proposed here.

WP5- Regarding the magnetic field, our proposed frequency coverage with an almost continuous coverage between 0.2 and 33 GHz puts us into an excellent position to utilise RM-Synthesis (Brentjens & de Bruyn 2005). With the polarisation capability of P-band we can attain a high resolution in Faraday-depth space (3 rad m^-2; see Heald et al. 2009). The line-of-sight magnetic field as observed with RM-Synthesis can be compared with three-dimensional magnetic field models (already in place; see Heesen et al. 2009), so that we can measure the direction of the magnetic field in the disc and halo. Also, by studying the degree of linear polarisation as function of frequency, and employing polarisation models (Schneider et al. 2014), we can (partially) correct for the effect of depolarisation due to the turbulent magnetic field and due to differential Faraday rotation by the regular field. This, in conjunction with our observations at 4.2 - 6.2 GHz, will allow us to measure the degree of linear polarisation and thus the strength of the ordered magnetic field, largely unaffected by Faraday depolarisation. As a bonus, we will be able to measure the degree of turbulence in the ISM below our spatial resolution (Heald et al. 2014) and compare the energy density in the turbulent ISM with that of the total B-field (Beck 2015).

Sample selection

In choosing the sample we are guided by the availability of the ancillary data provided by the SINGS and KINGFISH projects. Optical and IR data for these galaxies is unmatched with data from Spitzer and Herschel resulting in full knowledge of the IR SED in these targets, from the mid-IR through to the Rayleigh-Jeans tail. Their spatially resolved recent star formation activity has been mapped based on GALEX FUV and Halpha maps, both combined with Spitzer 24mu maps to correct for dust obscured SF activity. We selected those spiral galaxies from SINGS that were mapped by THINGS (Walter et al. 2008) to have matched data on the atomic gas phase and kinematics, and by HERACLES (Leroy et al. 2009, 2012) to trace the dense ISM.

We ensure the parameter space spanned by Hubble type, stellar mass, arm class (flocculent or grand design spiral arm structure), SFR, specific SFR (sSFR), and fractional polarisation is populated as evenly as possible, with 2-4 objects per (logarithmic) bin. The proposed sample is the absolute bare minimum required to sample evenly the parameter space.

Technical specification

We aim for the VLA observations at a sensitivity in units of SFR surface density of 2 x 10^-4 Msol yr^-1 kpc^-1 at 750 pc linear resolution, or 10” angular resolution at the most distant target. This is the sensitivity limit of the SFR density maps for our sample (Leroy et al. 2008). This is equivalent to 10 muJy beam^-1 at L-band when smeared to 10” resolution. This requirement sets the sensitivity limits across the various bands and configurations, requiring a few muJy beam^-1 across most of the bands observed. The analysis of individual SF regions requires the full resolution of ~2” across the entire frequency range. Most targets fit in a single L- or S-band beam, but at the higher frequencies mosaicking is required. This, plus the increased Tsys at the higher frequencies means that the larger fraction of observing time will be spent there, 1250 hours out of a total of 2100 hours for the full survey.

Regarding the GBT data, we will aim for comparable surface brightness sensitivity, in mK brightness temperature, as obtained in the VLA’s most compact configuration. We request time in the same bands as our VLA observations with the exception of P-band. Using OTF mapping A fully sampled map at Ka-band can be obtained in ~2hr, with gradually decreasing time demands towards the lower frequencies. This leads to an average time per galaxy of 4.5 hours (sum of exposure time in all bands) and a total time of just under 100 hours.

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Westcott, J., et al. 2018, MNRAS, 475, 5116","At present no need for special resources from the Observatory are foreseen other than the Observatory providing a repository for the Legacy products resulting from the proposed project (i.e., archival facilities). The team are experienced in reducing the kind of observations requested and have developed and adapted calibration pipelines to deal with multi-band, multi-configuration data.","The new eXtra-Large Proposal mechanism uniquely allows mapping of a complete sample of nearby galaxies across the entire radio SED. As mentioned above, the proposed sample is the absolute bare minimum required to sparsely sample the parameter space. Using the mechanism of a Large Proposal, at best one could hope to be awarded a few hundred hours which would allow observations from P- to C-band. Even though the number of configurations gradually drops when moving to the higher frequencies, the penalty imposed by the rapidly shrinking area of the primary beam and subsequent need for mosaicking, results in a time request that is beyond even the most generous of Large Proposals.

Covering the entire frequency range from P- to Ka-band crucially removes the need for Halpha maps to provide (a lower limit to) the free-free emission. Halpha has an intrinsic uncertainty of 0.2dex, even after the best possible calibration. The non-thermal emission thus corrected for any thermal contribution carries some of this uncertainty forward, in the end limiting the calibration of the non-thermal RC-SFR relation. Because the thermal and non-thermal emission are virtually extinction-free, the approach outlined in this project is far superior to anything else available, but it requires the generous time allocation available only through the mechanism of an eXtra-Large Proposal."
A Magnetic Field Census of Nearby Galaxies,mao@mpifr-bonn.mpg.de,Sui Ann Mao (MPIfR),"Rainer Beck (MPIfR), Andrew Fletcher (Newcastle)",1450,0,0,"This project aims to conduct the first homogeneous census of magnetic field properties in nearby galaxies and unambiguously link them to galaxy properties (type, stellar mass, rotation curve, star formation rate and star formation history). The lack of a homogeneous broadband polarimetric survey of galaxies calls for a much needed and first-of-its-kind proper census of galactic magnetic fields. We propose to conduct a broadband polarimetric survey at 1-8 GHz of a sample of >50 nearby (z<0.0075) moderately inclined galaxies, selected to have IFU data. This ensures that galaxy properties such as morphology, viewing geometry, intrinsic properties are all well defined and derived in a consistent fashion. This survey will inform us the typical 3D magnetic field properties in galaxies and the corresponding galactic conditions needed for galaxies to host a large-scale field. The survey will facilitate the first rigorous comparison between observations and theoretical predictions of galactic magnetic field properties. We ask for multi-configuration observations at L, S and C bands, totaling 22 hours per galaxy. Including overhead, 50 galaxies can be observed in 1450 hours.","Magnetic field is key to many astrophysical processes on a wide range of scales in the Universe, particularly in the interstellar medium of galaxies. However, the origin and evolution of magnetic fields in galaxies remains an unsolved fundamental question in astrophysics. To take a major step forward in unraveling this mystery, we aim to produce the first homogeneous census of magnetic field properties in nearby galaxies and unambiguously link them to galaxy properties such as galaxy type, environment, stellar mass, rotation curve, star formation rate and star formation rate history. While dynamically important galactic magnetic fields have been shown to play pivotal roles in processes that are closely linked to galaxy evolution, such as disk-halo interaction, gas accretion and galactic-scale outflows, the origin of magnetic fields in galaxies remains to be an unsolved fundamental problem in astrophysics. The leading theories of the origin of magnetic fields in galaxies are the fluctuation dynamo and the large-scale alpha-omega dynamo. Galaxies are the only astrophysical objects where it is feasible to directly observe the dynamo active regions and where dynamo theories can be tightly constrained by observations. Thus any advances we make in galactic magnetism will be of major importance for the wider field of cosmic magnetism. However, until now, rigorous comparisons between theoretical predictions and the observed magnetic field properties have not been possible due to the lack of homogeneous data sets: nearly all studies to-date consist of a single galaxy at discrete narrow frequency bands, thus when using a collection of these individual studies, both observational setups (e.g., instrument, resolution, frequency and depth) and analysis methods are vastly different among the sample. This could be one of the main reasons why there is a lack of correspondence between observed magnetic field properties and dynamo predictions using existing narrowband data (Van Eck et al. 2015).

With the advent of broadband backends and thus broadband polarimetry came a new era for mapping 3D magnetic field structures in galaxies: as we have recently demonstrated using several nearby galaxies (M51: Mao et al. 2015, Kierdorf, Mao et al. in prep, Mulcahy, Beck et al. 2018 ), that we can now use new polarimetric analysis methods to characterize the magneto-ionic medium (large and small scale magnetic field properties, particle distributions/scale heights etc.) in ways that were not possible before using just narrowband data.

The lack of a homogeneous broadband dataset calls for a much needed and first-of-its-kind proper census of galactic magnetic field properties in the nearby Universe. We propose to conduct a broadband polarimetric survey of a sample of >50 nearby (z<0.0075) galaxies, selected to have integral field unit data from either the CALIFA (Sanchez et al. 2012) or the DISKMASS (Bershady et al. 2010) surveys. A statistically substantial sample size (at least ~ 50 galaxies) is needed to be able to robustly identify any magnetic field properties trends against galaxy properties. This uniquely defined sample with existing IFU observations ensures that galaxy properties including galaxy morphology, viewing geometry, intrinsic properties such as star formation rate and its history, ionized gas rotation curve, and stellar mass etc. in our sample are all well defined (and were derived in a consistent fashion). The proposed survey will inform us the (1) typical 3D large-scale magnetic field in galaxies, including the occurrence of large-scale magnetic field reversals; (2) typical properties of random magnetic fields in the sample (e.g. the characteristic scale, their power spectrum and the (an)isotropy of the random field). It will allow us to classify galaxies according to their magnetic field properties for the first time and observationally derive the galactic conditions (such as the minimum rotation velocity, minimum amount of shear, specific star formation history, any star formation rate threshold etc..) needed for galaxies to host a large-scale magnetic field. For each galaxy, we will use the observed galaxy properties to generate an individual large-scale dynamo model to predict its large-scale field. We will then generate synthetic polarization observations based on the dynamo prediction and compare with the observed broadband polarization data. To take into account of effects dynamo theories do not capture, we will in addition produce synthetic polarization observations of galaxies with matched galaxy properties selected from cosmological MHD simulations.
In order to reach similar surface brightness sensitivity as existing polarimetric observations, and to ensure that the physical scale corresponding to one resolution element is at least 1 kpc (in order to minimize beam depolarization effects), we aim to reach a sensitivity of 3uJy/beam at 6” resolution for galaxies at z<0.0075.

We request L, S and C band frequency coverage. From our experience, this broad lambda^2 coverage is necessary for the success of Faraday tomography. We further assume that as we move from low to high frequency bands, the spectral index effect is compensated by less amount of wavelength-dependent depolarization, so we set our target sensitivity at ~ 3uJy/beam at 6” resolution at all bands.

We note explicitly here that high angular resolution and high surface brightness sensitivity is needed for this survey, and thus requires dedicated observing time instead of using upcoming broadband survey data: VLASS is simply not deep enough for this study, and POSSUM and APERTIF have insufficient sensitivity and have too large of an angular resolution to overcome beam depolarization at these distances. The Jansky VLA is the instrument of choice not only due to its access to the northern sky (target galaxies are mostly located in the SDSS footprint), but also because of its continuous frequency coverage from 1-8 GHz: it has legacy values even in the SKA1 era - SKA1-MID top priority deployment will only cover a fraction of this frequency range: band 2 (1-1.7 GHz) and band 5a (4.6-8.5 GHz), while the key frequency range from 1.7 GHz to 5.2 GHz (Band 3 and 4) is not covered and will only be deployed if funding for an SKA1 upgrade is made available.

As the target galaxies have angular sizes from 45”-80”, care has to be taken so that all extended emission is captured - this requires multi-configuration observations. The sensitivity requirement translates into L band on-source time of ~15h13mins at B and ~21 mins at C configurations; S band on-source time of ~ 3h42mins at B and ~20 mins at C configurations; and C band on source time of ~ 2.5 hours in C configuration. This sums up to ~ 22 hours on-source per galaxy. Including overhead, we estimate that 50 galaxies can be observed with a total observing time of 1450 hours.

These observations will not only generate legacy spectropolarimetric data for the main science goal on galactic magnetism, it will produce valuable ancillary data for the wider astronomy community as well. For the L band observations, we will simultaneous observe the 21cm line to map out spatially resolved HI kinematics of these galaxies and we will observe various radio recombination lines simultaneously with S and C band observations. The neutral hydrogen kinematics information will further facilitate comparisons with rotation of other gas phases (CO, ionized gas, see e.g. Levin et al. 2018) While polarization is the main focus of this survey, Stokes I information of galaxies in the sample is highly valuable as well for the study of star formation — spatially resolved radio-FIR correlation can be investigated in different regions in each galaxy: different slopes of the correlation encode important information about the underlying physics of star formation, such as the relationship between gas density and field strength, and gas density and the star formation rate.

Data will be reduced using a dedicated pipeline developed for broadband diffuse polarized emission, producing combined array Stokes I Q U data cubes across L S and C bands. RM synthesis will be conducted, as well as the analysis and fitting complex polarization as a function of wavelength-squared across the entire galaxy. We plan to release data products of the survey online, containing basic total intensity and polarization data cubes as well as an atlas containing 3D rendering / visualization of magnetic fields in each individual galaxies.",--,"The proposed science goals cannot be achieved through standard TAC process because a statistically substantial sample size (at least ~ 50 galaxies), and hence over 1000 hours of observing time, is needed to robustly identify any magnetic field properties trends against galaxy properties."
Deep GBT Observations of Chemical Complexity At the Early Stages of Star Formati,bmcguire@nrao.edu,Brett A. McGuire,"Nadia Balucani
Andrew M. Burkhardt
Paola Caselli
Cecilia Ceccarelli
Claudio Codella
Eric Herbst
K.L. Kelvin Lee
Michael C. McCarthy
Anthony J. Remijan",0,4000,0,"The recent detection of benzonitrile (C6H5CN) - the largest molecule every seen with radio astronomy - in the cold, starless cloud TMC-1 has demonstrated that there is a substantial, previously unknown reservoir of molecules at the earliest stages of star formation. A hidden population of carbon-rich species like C6H5CN would have significant consequences on the growth and influence of dust and grains in nascent planetary systems. The large size of these molecules, and cool environments in which they are found, dictate low frequency (<50 GHz) observations, making the GBT the only facility with the sensitivity and spectral coverage capable of doing this science. Here, we propose a series of exceptionally-sensitive spectral line surveys in Ka and Q-bands with the GBT of eight sources across the evolutionary spectrum from starless cores to very young protostars. Unlocking this lurking reservoir is only possible with these exceptionally deep observations. Ensuring that the underlying complexity is not a rare occurrence, and is indeed an integral part of the star formation process, requires a much larger sample size than can be reasonably undertaken even as part of a Large Project","A total of 204 molecules are known to exist in interstellar and circumstellar environments. The majority (66%) of these are small (<6 atoms) and thought to form through gas-phase ion-neutral reactions that are efficient in a number of environments. Larger molecules are predominantly thought to form through neutral-neutral reactions, often involving radicals, on the surfaces of grains. These molecules are thought to largely be trapped on these grains until the thermal radiation from a newborn star heats the surface sufficiently to liberate them into the gas phase. Thus, the prevailing wisdom has been that chemical complexity is contained in the solid-phase until well after star formation begins.

Our recent detection of the largest and arguably most complex molecule ever seen by radio astronomy (benzonitrile; C6H5CN) in the cold, dark, starless cloud TMC-1 challenges these assumptions. Aromatic molecules like benzonitrile and its larger cousins the polycyclic aromatic hydrocarbons (PAHs) are suggested to contain up to 25% of all interstellar carbon - a massive elemental reservoir. Many of these PAHs are also large enough to be the charge balance carriers in interstellar environments, the catalytic sites of molecular hydrogen formation, and the seeds of dust formation. Thus, these large carbon molecules are not only chemically significant, but are essential components of the physical and dynamical processes driving interstellar evolution.

Until very recently, the primary production method for these large species was thought to be 'top-down,' meaning that late-stage stars output a carbon 'soot' that is degraded to PAHs by photodestructive processes. This theory is supported by the fact that we observe these species predominantly in photodissociation regions (PDRs) and in and around AGB stars and planetary nebulae. Yet, we have detected benzonitrile in a cold, dark, starless cloud before star formation has even begun. This suggests that 'bottom-up' synthesis of these large molecules from small precursors formed by gas-phase reactions is not only possible, but likely quite efficient. It also means that there is potentially a vast reservoir of previously undetected and unconsidered large carbon species present at the very beginning of star formation, and influencing that process throughout the entire evolutionary cycle.

If there is such a reservoir, why have we only just now seen it, and why did it take such sensitive GBT observations? Indeed, the detection of benzonitrile required substantial integration time with the GBT, and the overall column density was quite low. This is because while the aggregate population of large molecules has the potential to be quite vast, the chemistry leading to them is so diverse that the fractional abundance of any one individual species is low, making detection challenging and expensive.

Further complicating the issue is that because we have so few detections of these large molecules, our understanding of their chemistry is quite limited. This makes selecting individual species for targeted observations nearly impossible, necessitating even more expensive blind spectral line surveys. We recently received a Large Project to survey a portion of the GBT's coverage (18-27.5 GHz) toward TMC-1 (PI: McGuire), and have submitted a set of pilot observations of two young protostars to do the same in a much smaller portion of Ku-band (13.5-15 GHz) (PI: Codella). Yet, even with the Large Project, we are limiting ourselves to a relatively narrow slice of frequency coverage in a potentially unique source. To truly understand the prevalence and influence of these large molecules on the earliest stages of star formation requires a larger sample size, and substantially expanded frequency coverage.

As collapse begins, the effective emitting area of the source shrinks, making observations at the higher ends of the GBT's capabilities appealing, for better matches with beam sizes. An effective balance between line intensity (peaking typically between 15-40 GHz for large molecules at temperatures typical fo these regions) and beam size (best at W-band, but reasonably well-matched down to about K-band), the optimal observational parameters would seem to be a survey of Ka- and Q-bands. The linewidths in these sources are narrow (0.3-1.5 km/s), and the populations of individual large molecules low, requiring high sensitivity (1-3 mK). The end result is a requirement of 500-1000 hours per source to cover most of Ka and Q-bands at the required resolution and sensitivity.

This is an approachable number for a Large Project, but only on one source. To even begin to study the effects of these large molecules requires a larger sample size, pushing the needs well beyond a Large Project. For an effective eXtra Large Proposal, we could foresee targeting ~8 sources with 500 hours of observation each over the course of 8 semesters, covering most of Ka and Q-bands. A representative list of sources would be:

TMC-1 (Dark Cloud)
Lupus 1-A (Dark Cloud)
MC 27 (Warm Carbon-Chain Chemistry Source)
Serpens 1a, 1b, and 2 (Cusp of Dark Cloud -> Protostar Stage)
L1544 (Pre-stellar Core)
IRAS 16293 (Protostar)

The results would be an invaluable set of line survey data, made publicly available in its fully-reduced form, across the stages of early evolution.","Operator-driven observations. This type of eXtra Large Project is simply not possible to run on remote observing sessions from team members.

A dedicated system for storing and disseminating fully reduced data products to the public, preferably with a GUI web interface for browsing the data online before downloading.",
VLA-GBT WideBand Galactic Plane Survey,fschinze@nrao.edu,Frank Schinzel (NRAO),"L. Anderson (WVU), S. Bhatnagar (NRAO), G. Castelletti (U. Buenos Aires), T. Clarke (NRL), D.A. Green (Cambridge, UK), P. Jagannathan (NRAO), N. Kassim (NRL), R. Kothes (DRAO), W. Peters (NRL), D.J. Pisano (WVU), U. Rau (NRAO), A. Roshi (NRAO), L. Supan (U. Buenos Aires)",5500,700,0,"We express interest to perform a wide-band continuum and spectral line Galactic plane survey in the L/S-band (1-4 GHz) in C/D array, exploiting the power of the VLA's WIDAR correlator for simultaneous high resolution observations of the HI 21cm line, all four OH transitions, 18 recombination lines (both H and C), the 1066 MHz transition of Formaldehyde, and potentially other lines accessible through S-band. All other existing surveys of the Galactic plane in the radio bands are narrow-band surveys. This new survey, using the wide-band capabilities of the Jansky VLA, besides being able to provide significantly deeper and higher resolution images (up to 10x improvement over CGPS in sensitivity and 2-3x improvement in resolution), will for the first time also provide spectral index (SI) and rotation measure (RM) maps. The SI and RM maps will be the new scientific products (as against improvements over previous surveys) not available via existing surveys. To allow sensitivity-limited wide-band reconstruction of the omnipresent extended emission and the spatially resolved spectral distribution in the plane, VLA observations would be combined with similar observations with the GBT.","Large-area surveys of the Milky Way at many wavelengths have shown that the Galaxy is both dynamic and complex, on scales ranging from arcseconds to many degrees. The radio continuum is no exception, being comprised of a rich mix of thermal and non-thermal emission, tracing young stars and supernova remnants, shock waves and magnetic fields. The very richness that makes radio images interesting makes their interpretation challenging since the low radio opacity means that a radio image represents the sum of all emission regions along the line-of-sight - especially in the Galactic Plane. These challenges make the existing narrow-band radio surveys difficult to interpret. A VLASS white paper was submitted proposing a VLA-GBT Wide-band Galactic Plane survey (Bathnagar et al. 2013b), which formed the basis of this EoI.

In principle, radio observations can be used directly to disentangle all these effects. Mapping the frequency dependence of the brightness distribution can distinguish free-free from synchrotron emission, mapping polarization at high frequency resolution can constrain the RM along the line-of-sight and mapping the distribution of HI 21cm line and radio recombination lines (RRL) can help map out the three-dimensional distribution of the gas in the Galaxy. All of these however require wide instantaneous bandwidth observations.

To date, only a fraction of this potential has been realized. Existing unbiased radio surveys mostly cover a narrow frequency range with continuum emission a happy afterthought: The Canadian Galactic Plane Survey (CGPS), Taylor et al. (2003), the The Southern Galactic Plane Survey (SGPS), McClure-Griffiths et al. (2005); Haverkorn et al. (2006) and the VLA Galactic Plane Survey (VGPS); Stil et al. (2006). While these surveys provide continuum images, the continuum sensitivity of these surveys is severely limited by this narrow total bandwidth. Such narrow bandwidth data also rule out any possibility of deriving a systematic map of the continuum SI mapping, RM mapping or building line sensitivities by stacking multiple RRL transitions.

The Jansky VLA's WIDAR correlator and new wide-band wide-field imaging algorithms together now open up the possibility of lifting all these restrictions. We can record data for continuum emission over wide bandwidths, with high spectral resolution and full polarization information, while simultaneously obtaining much higher spectral resolution on interesting parts of the spectrum. The MS-MFS (Rau et al. 2009; Rau 2010), A-Projection (Bhatnagar et al. 2008) and WB-A-Projection (Bhatnagar et al. 2013) algorithms together enable wide-band wide-field imaging that simultaneously give high quality continuum and SI maps of regions with complex emission. Algorithms for all components either exist in production software or are currently undergoing commissioning by members of this group. Wideband A-W Projection to handle A and W together in a mosaic, Multi-term solutions for spectral index recovery, Wideband single dish+interferometer joint reconstructions, Full-Mueller AWProjection and parallelization for all of the above (Jagannathan et al. 2017, 2018). In addition to automated flagging during the imaging stage. All these are also being pushed forward to production through the VLASS.

A pilot observation was already performed, obtaining a wide-band mosaic of the CTB80 field with the EVLA. It was also observed in a wide-band mode with the GBT. The EVLA data has been processed for wide-band continuum imaging and a publication is imminent. In addition, the HI/OH/Recombination line survey of the Milky Way (THOR; http://www2.mpia\-hd.mpg.de/thor/Overview.html), observed 15<l<67 deg. and |b|<+/-1 deg. in HI, four OH, and 19 H alpha recombination lines as well as in the L-band continuum from 1--2\,GHz. These sets of observations can be used as pilots for a survey that covers the entire Galactic plane reachable by the VLA. The scientific merit of such a wideband-widefield Galactic plane survey can be summarized in four themes.

1. Continuum and spectral index imaging

Supernova (SNe) explosions and their remnants (SNRs) have a profound effect on the morphology, kinematics, and ionization balance of galaxies, and possibly trigger new generations of star formation. In our own Galaxy, SNR-generated cosmic rays provide at least 1/3 the energy input to the ISM. However, based on statistical studies of predicted SNe rates, there should be about 1000 SNRs in our Galaxy (Li et al. 1991, Tammann, Loeffler, & Schroeder 1994) than are currently known (294; Green (2014)). In addition to this deficit in the total count, current catalogues lack specifically young (and hence small) and old (and hence extended and low surface brightness) remnants due to well known selection effects addressable by this survey. The missing remnants are thought to be concentrated toward the inner Galaxy where the diffuse synchrotron emission from the Galactic ridge and HII regions cause the most confusion. Surveys of limited regions along the plane with sufficient surface brightness sensitivity have already detected the tip of this hidden iceberg (Brogan et al. 2006).

Observations of low-frequency (<2 GHz) Radio Recombination Lines (RRLs) established the presence of extended low-density ionized gas (DIG) in the inner Galaxy (|l|<50 deg.) (Lockman 1976; Anantharamaiah 1985; Pedlar et al. 1989), Roshi & Anantharamaiah (2000) showed that the line emission is clumpy (at scales of a few arcmin) but extended (few deg. scale). Studies of radio free-free emission suggest that the DIG is ionized via absorption of >70% of the radiation from OB stars, while 'classical' HII regions absorbing the rest (Mezger 1978; McKee & Williams 1997; Murray & Rahman 2010). Thus, while the DIG plays an important role in the evolution of the ISM, we still do not know how the photons from OB stars travel long distances beyond the 'classical' HII regions to ionize the DIG. A detailed observational study of the morphology of the DIG can give clues to answer this question and test the various morphological models proposed in the literature (Shaver 1976; Anantharamaiah 1986; Heiles et al. 1996; Murray & Rahman 2010). The expected thermal emission from DIG is in the range 0.8-4.8 K.

Unbiased wide-band continuum and spectral index mapping can separate thermal and non-thermal emission and help identify the missing populations of SNRs as well as differentiate the thermal nature of the DIG from diffuse non-thermal emission at high significance.

2. RM-synthesis

Spatially resolved RM maps provide not only the spatial distribution of Faraday rotation screens, but also a handle on the Faraday depth distribution by separating the emission at different depths. Smooth background polarization is produced everywhere in our Galaxy and it is Faraday rotated while it is propagating through the Galaxy. With RM synthesis we can determine the Faraday rotation seen by different sources of polarized emission along the line of sight. With the large number of compact background sources seen through the Galaxy, we can also separate their internal Faraday rotation from the foreground rotation, produced by our Galaxy, using RM synthesis.

3. Spectral Line Science

RRL: In the 1-2 GHz frequency range, the hydrogen alpha RRLs from classical HII regions (i.e T~7000K) are expected to be 1-2% of the continuum. At the sensitivity level we expect to attain, lines will exceed 5 sigma for several known sources in the field-of-view. Because we will observe 18 lines over the frequency range, we will also be able to separate optical depth effects and non-LTE effects. Note, that for weaker line search, we will be able to stack sub-bands to improve sensitivity at the cost of losing information about variation of non-LTE effects.

OH: The 4 L-band lines of OH are very useful probes of the interstellar medium. The 1665 and 1667 MHz (main lines) are often masers in regions of high density and excitation in regions of star formation. The 1720 MHz masers are frequently found on the rims of supernova remnants, while the 1612 MHz masers are often found in the circumstellar shells around Red Supergiants. Absorption in all 4 lines occurs in less dense gas along the line of sight to radio sources, and all four lines are also detected in cold dust clouds. The versatility of the WIDAR correlator permits simultaneous observation of these lines to sample a wide range of interstellar conditions.

H2CO: We propose to include the 4(22)-4(23) transition of H2CO at 1.066 GHz in one narrow subband. This line will not be found in the general ISM because both the upper and lower states can also decay by spontaneous transitions with lifetimes ~2000s. Therefore, they will only be populated in regions with densities of ~10^6 cm^-3 and temperatures ~100K, i.e similar to regions of mainline OH masers and H2O masers. The excitation of closely spaced K-doublets is delicate, and we have no prediction for the relative populations of the 4(22) and 4(23) levels.

HI: While data from the CGPS, SGPS and VGPS HI surveys exist, our observations will provide higher brightness sensitivity data on the HI line. We also want to observe lines, in particular the HI line, in linear polarization as well. Data from existing surveys does not have spectral line data in full polarization, typically due to limitations of the correlator resources. Since HI emission is unpolarized we have the unique opportunity to observe very clean absorption profiles from sources that are too faint to produce reliable absorption signals in total power. HI absorption in total power is limited by foreground fluctuations of a few Kelvin (~6K) produced by clouds smaller than the beam. Therefore, only HI absorption profiles of sources with at least 20 K peak brightness can produce significant absorption in total power, no matter how long you integrate. To get a reliable absorption profile we probably need 50 -- 100 K peak brightness and even those profiles are sometimes ambiguous. This is in particular true for extended sources. In polarization those profiles are noise limited and there is no ambiguity caused by small-scale fluctuations. A preliminary study of this was done by (Kothes et al. 2004). They did detect HI absorption in polarization of SNRs that have ~1 K peak brightness in polarization. This method would be great to determine distances to Galactic SNRs and probe the ISM with polarized extragalactic sources.

4. Commensal science

A survey of this scale would greatly benefit the commensal activities at the VLA, where corresponding continuum data could be collected simultaneously with VLITE for continuum/polarimetric imaging of the Galactic Plane at 330 MHz, as well as fast pulse searches (ms-Pulsars) through VLITE-FAST. In addition, the Realfast backend is able to simultaneously explore slower Pulsars and Rotating Radio Transients focusing on the Galactic Plane.

Altogether, this survey would lead the way for Galactic science into the ngVLA-era and provide a complementary data base for Galactic plane surveys planned by the SKA.

OBSERVING STRATEGY

The primary frequency range of the survey be the L-Band covering the 1-2 GHz range, with an optional addition of 2-4 GHz to widen the continuum frequency coverage. Thus, covering a total frequency range of 1-4 GHz. Such a L- and S-Band survey will be better optimized for mapping both thermal and non-thermal emission, various line transitions and better SI and RM mapping. The total area of the sky to be imaged is about 660 sq. deg, which would cover the original survey area of CGPS (74.2<l<147.3 deg.; -3.6<b<+5.6 deg.). This would require about 7260 pointings to allow enough overlap for widefield mosaicking with 10 min per pointings. The THOR survey already observed 54 square degrees at L band, which data would be reprocessed in the context of this survey and thus will not need to be reobserved.

To achieve an RMS sensitivity limit of 35uJy/beam a total amount of 1331 hours at L band in D+C configurations each and 2874 hours at S band in D configuration are required (assuming 10% overheads). This would also achieve line sensitivities of 9 and 17 mJy at 1 and 2 GHz respectively. A Faraday depth probing of 10-25000 rad m^-2 and a spatial resolution of about 15-25 arcseconds, a factor of 3-4 higher than CGPS. GBT data would supplement short spacings to adequately image large scale structures, to provide a zero spacing flux, and to boost the surface brightness sensitivity of the survey. The GBT frequency overlap at L and S band does not perfectly match that of the VLA, however it would still provide the needed information to image large scale structures especially in the context of joint wideband reconstructions. To reach the confusion limit over the survey area, we estimate that for L band we would require about 100 hours of GBT observing time, while for S band the request would be about 600 hours. If this were to go forward as proposal, a detailed study of the required GBT observing time would be provided, including the potential use of phased-array feeds (PAF) that would dramatically reduce the needed observing time. Low-noise PAF is a realizable technology now (Roshi et al. 2018) and the survey would greatly benefit by having such a PAF on the GBT. Were the GBT not included with VLA observations, the VLA only time request would increase by about a factor of 9 to achieve similar brightness sensitivities.

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Stil, J. M., et al. 2006, Astron. J., 132, 1158
Tammann, G. A.; Loeffler, W. & Schroeder, A. 1994, ApJS, 92, 487
Taylor, A. R., et al. 2003, Astron. J., 125, 3145","The challenges lie primarily in the computing cost and wide-band polarization imaging. Accurate RM mapping requires wide-band polarization calibration and accounting for any frequency and direction-dependent instrumental effects. While algorithms and procedures for full-polarization calibration and imaging also exist, these need to be tested carefully and some research and development might be needed by NRAO to enable CASA to make use of these new algorithms in an efficient manner. Imaging algorithms better optimized to use the available bandwidth for RM mapping of extended emission as well are under development and R&D efforts could include porting imaging algorithms to make use of GPUs. This survey will greatly benefit from progress made in this area by VLASS. Due to large data volumes and higher computing involved, data processing will have to be deployed on HPC platforms. The impact on NRAO infrastructure could be the increased use of storage for staging and archiving of survey data products, as well as part of the data processing, where partnerships with other institutions and funding streams will be explored to support this survey were it to go forward. Another area where observatory resources are needed are related to science ready data products. The survey would require to tune the calibration/imaging pipelines to generate in particular spectral line data products and to adjust pipelines to generate image products using newly developed imaging algorithms.","The outlined survey was presented as a white paper prior definition of the scope of VLASS (Bathnagar et al. 2013b). A scaled down version of a Galactic plane survey was originally part of the final VLASS proposal but did not receive favourable ratings due to significant flaws in its presentation and scope. It lacked a justification of required angular resolution/sensitivity to large angular structure and omitted polarization. These flaws would all be addressed by the survey outlined here. Furthermore, the outlined survey is of a scale where it is difficult to compete with smaller scientifically more focused proposals that would be traded off against a proposal of this scale. However, the scientific merit of a large survey could be magnitudes higher than that of smaller projects due to its multitude of applications and scientific uses for a larger fraction of the community.

A separate call for proposals that targets projects that would benefit the wider community, *independent of the requested amount of observing time*, evaluated against each other, might be better suited for large surveys, monitoring projects, and other projects that would cater to the wider community. The results of such observations could generate significant multiplier effects and are likely to increase the impact of observations with the VLA, VLBA, or GBT in the future. Important criteria, besides scientific merit, for evaluation of such community driven X proposals should be: 1) the expertise of the proposing group, 2) the likelihood that the PI driven project would deliver data products to the community in a useful and timely manner, 3) the impact on the observatory resources, 4) the interaction with regular PI driven science projects."
The VLA Extragalactic Database for Galaxy Evolution (EDGE): A Spatially Resolved,wongt@illinois.edu,Tony Wong,"Alberto Bolatto, Veselina Kalinova, Dyas Utomo, Dario Colombo, Adam Leroy, Fabian Walter, Sebastián F. Sánchez, EDGE-CALIFA collaboration",3000,100,0,"We propose to complement the Calar Alto Legacy Integral Field Area (CALIFA) survey with resolved HI imaging with the Jansky VLA. CALIFA has observed ~900 galaxies at redshifts <0.03 with the PMAS/PPak integral-field spectrograph (IFS) to derive properties of the stellar populations and ionized gas, and the main CALIFA sample is designed to be statistically representative of luminous nearby galaxies. 126 of these galaxies, selected based on WISE infrared flux, have already been imaged in CO emission with the CARMA EDGE survey. The VLA X-Proposal we propose would obtain resolved HI imaging for the ~500 completed galaxies in the main CALIFA sample, preserving the representative character of CALIFA. The survey would be a uniquely powerful probe of how the distribution of HI, and dynamical mass generally, relates to star formation, galaxy structure, and chemical enrichment. Combining IFS data, resolved CO data for the central regions of galaxies, and resolved HI data extending beyond the optical disk, the resulting database would synthesize key information on the baryonic content and gravitational potential of galaxies across a wide range of types and environments.","The changing rate of star formation has been the main driver of galaxy evolution over the past few Gyr (e.g., Speagle et al. 2014; Garcia-Benito et al. 2017; Sanchez et al. 2018), and a great deal of effort has been invested in understanding how the star formation rate is regulated by (and in turn may regulate) the cold gas supply (Lilly et al. 2013). The molecular gas in which star formation occurs has a current depletion time of at most ~2 Gyr, so the atomic gas is the ultimate reservoir for star formation. Surprisingly, while the molecular to atomic ratio varies strongly within galaxies (e.g., Bigiel et al. 2008), both HI and H_2 content scale roughly linearly with SFR, averaged globally (Schiminovich et al. 2010, Saintonge et al. 2011). This suggests a tight coupling between the total atomic gas content and star formation, despite the two often exhibiting very different radial distributions.

To investigate how the resolved properties of the HI relate to those of the stars and ionized gas, we will propose a VLA extra-large survey, targeting the main (i.e., objectively selected) sample of CALIFA galaxies observed with full spectroscopic coverage. HI radial profiles and fluxes will probe the gas supply, while HI rotation curves will probe the dark halo potential. The large database we obtain will be used, among other things, to study the influence of environment (including close companions and ongoing mergers) on the average and spatially resolved star formation efficiency as a function of halo mass. From simulations, there is an indication that the SFE of the galaxies peaks at an intermediate halo mass (~10^12 M_sun), but this still needs to be proven by observations such as our detailed IFU-CO-HI survey could provide.

In preparation for this survey, we begun gathering archival HI spectra from recent surveys (e.g. ALFALFA, Haynes et al. 2011), and supplemented them with our own GBT observations of CARMA-observed sources. With the VLA, in order to achieve a synthesized beam of 6"", corresponding to 0.8 kpc for a typical CALIFA galaxy, while reaching a 3-sigma HI column density of 5e20 cm^-2 per 20 km/s channel, we will observe each galaxy for 5 hours in the B array and 1 hour in the C array. For a sample of 500 galaxies, the total time request would be about 3000 hours. A modest amount of time (~100 hours) for GBT pointed observations may also be requested.

At the same time, we will propose deep CO integrations with the Large Millimeter Telescope (LMT) to constrain the molecular gas contents of galaxies that have not been observed with CARMA. We are currently also seeking ALMA time to observe about 200 CALIFA galaxies visible from the Southern hemisphere. Combining the properties of stars (CALIFA), ionized gas (CALIFA), atomic gas (GBT+VLA), molecular gas (CARMA, LMT, ALMA), and the dark matter halo (VLA) in a statistically significant sample of ~500 galaxies would offer unprecedented leverage to study galaxy evolution at z~0.

Q. Why not use the VLA THINGS data?
A. While THINGS has provided exquisite resolution and sensitivity for 34 nearby galaxies, and has pushed the limit of what is currently possible with the VLA, it primarily consists of a handful of the nearest and most actively star-forming disk galaxies. Our survey is complementary in providing a much larger number of galaxies across the star-forming main sequence (and beyond), albeit at coarser angular resolution. More importantly, the CALIFA sample is statistically representative of the full population of galaxies in the Local Universe, for M*>10^9 Msun (Walcher et al. 2014). The large angular size of THINGS galaxies is also a challenge for coverage via optical and CO spectroscopy, although excellent data sets are being obtained in many cases with ALMA and MUSE (e.g., PHANGS collaboration).

Q. Why not use a single-dish HI survey like ALFALFA or xGASS?
A. Although HI spectroscopic surveys have provided powerful statistical knowledge of the gas content of galaxies, they only capture the total gas content, and cannot fully exploit the resolved optical and CO spectroscopy provided by CALIFA and EDGE. The spatially resolved information needed to study chemical evolution, the fueling of star formation, gas inflows and outflows, and the dark halo mass profile can only come from the VLA. Moreover, galaxies with strong continuum emission tend to exhibit complex absorption profiles in HI which are difficult to disentangle from emission when observed with a large single-dish beam. The upgraded VLA correlator now provides excellent sensitivity for both line and continuum emission.

Q. Why not use another IFS galaxy survey for target selection?
A. The four major IFS galaxy surveys (either on-going or finished), in terms of number of galaxies and statistical significance, are Atlas3D (Cappellari et al. 2011), CALIFA (Sanchez et al. 2012), MaNGA (Bundy et al. 2015), and SAMI (Croom et al. 2012). Each has its own unique strengths, but the surveys besides CALIFA are less ideal for complementary HI and CO observations, due to the selection of mostly quiescent galaxies (Atlas3D), a large range in redshift (MaNGA), or limited spatial coverage outside the central regions (SAMI). For the proposed project, CALIFA provides the best compromise between spatial coverage, physical spatial resolution, projected FoV, and redshift range.",N/A,A conventional Large Proposal would only cover of order 50 galaxies and would not be a significant step beyond existing surveys.
Stellar SiO Masers in the Bulge - Parallax and Proper Motion,ylva@unm.edu,Ylva Pihlstrom,"Huib Jan van Langevelde
Luis-Henry Quiroga-Nunez
Lorant Sjouwerman
Mark Claussen",100,0,3500,"We propose an approximately 3,500 hour VLBA program to determine proper motions and/or parallax distances to a set of 250 red giant SiO maser stars. The SiO maser stars are identified from the Bulge Asymmetries and Dynamical Evolution (BAaDE) 43 GHz SiO maser survey at the VLA, and targets will be selected in order to highlight both typical orbits and kinematical populations, as well as focusing on individual kinematical outliers. These observations will provide details about stellar orbits in the Galactic Bulge and Bar regions, thereby testing and improving models about the dynamicalstructure. With the VLBA we will be able to a) determine the positions, proper motions and parallaxes (thereby distances and 3D velocities), and b) determine the 3D orbit family of the objects (circular, radial/very elongated, x2). We note that this is complementary both to Gaia, which cannot measure parallax distances for most of our targets due to obscuration as well as not reaching the bar, and to the BeSSeL project, which focuses on distances to starforming regions (and spiral arms) within the Galaxy.","1. The Bulge Asymmetries and Dynamic Evolution (BAaDE) Project

The central Galaxy is now understood to be dominated by a massive bar, based on infrared morphology (e.g., Dwek et al. 1995, ApJ, 445, 716), spatial distribution of red clump stars (e.g., Babusiaux & Gilmore 2005, MNRAS, 358, 1309), maser stars (Habing et al. 2006, A&A, 458, 151), and dynamics of red giants (e.g., Kunder et al. 2012, AJ, 143, 57). Indeed, an N-body model in which the bar forms via dynamical buckling from a preexisting massive disk fits the red giants dataset so well that less than 10% of the bar might be in the form of a classical bulge, a result that is sustained by the clear demonstration of cylindrical rotation, a signature of strongly triaxial or boxy bulges (Howard et al. 2008, ApJ, 688, 1060). Recently, compelling evidence emerged for an additional X-shaped structure, similar to that seen in a number of extragalactic edge-on boxy bulges (e.g., Wegg & Gerhard 2013, MNRAS, 435, 1874). It has proven hard to isolate the population responsible for this structure and to study the kinematics (Vasquez et al. 2013, A&A, 555, 91). However, there is growing consensus that the X-shaped structure is dominated by the metal rich bar (Ness et al. 2012, ApJ, 756, 22).

Optical surveys of the bulge are a powerful approach to learn about the populations and dynamics in the less reddened and obscured regions at Galactic latitudes |b|>4 degrees. To a great extent, surveys in the optical/infrared bands have begun to reach impasses that cannot be easily resolved with increases in sample sizes. Red giant maser sources, as can be exploited with the Atacama Large Millimeter Array (ALMA), the Very Large Array (VLA), and the Very Long Baseline Array (VLBA) offer a bold new approach to address the most pressing problems in the study of the bulge/bar. Our goal is to produce samples of
radio-detected red giants that are comparable to the 10,000-30,000 stars in optical surveys. By using SiO masers, detectable in red giants spanning a wide range in luminosity, we have the possibility of densely sampling the highest extinction, most crowded regions of the Milky Way: the Plane and Galactic Center.

Using the VLA and ALMA, we are in the midst of the largest SiO maser survey ever of 28,000 red giant stars (the Bulge Asymmetries and Dynamical Evolution survey, BAaDE), pushing into these regions that are in principle not reachable with optical surveys (Sjouwerman et al. in prep.). At the SiO maser frequencies (43 & 86 GHz) we are not hindered by extinction, and extremely accurate line-of-sight stellar velocities (1 km/s) and positions are determined. The number of sources will be large enough to trace complex structures and minority populations. The velocity structure of these tracers is to be compared with the kinematic structures seen in molecular gas near the Galactic Center, and thereby highlight kinematically coherent stellar systems, complex orbit structure in the bar, or stellar streams resulting from recently infallen systems. Modeling of the bar and bulge dynamics has begun using the new kinematic information in the inner Galaxy region (Trapp et al. 2018, ApJ, 861, 75).

In particular, our survey also identifies sufficiently luminous SiO masers suitable for follow-up orbit and parallax determination using Very Long Baseline Interferometry (VLBI). Our specific aim is to determine, in detail, orbits of stars supporting the stellar bar. In this Expression of Interest (EoI) we outline the VLBI part of the BAaDe project.

2. VLA project status

At this time all VLA observations are completed (of about 19,000 stars), while ALMA observations of the far side of the bar still are underway. For this EoI though, we only focus on sources from the VLA sample, observable also with the VLBA. The VLA pipeline data reduction is expected to be completed by the end of 2018. Our direct detection rate (without doing imaging) of SiO maser stars is over 60%. Most targets display both the v=1 and v=2 lines, and some are detected in up to six different SiO lines. Updated project results can be found on our project web page www.phys.unm.edu/~ylva/baade.html.

3. The BAaDE VLBA program

While the VLA data directly can be used to test dynamical models statistically, much more details can be derived if distances and proper motion information were available. The second part of BAaDE therefore includes a VLBA study, with the ultimate goal to determine orbits and distances of stars in the inner Galaxy. Note that neither Gaia (nor its proposed successors) can reach the bar, thus this program will provide unique information about the inner Galaxy. With the VLBA our aim is to observe at least 250 targets (3500h) to:

1) determine positions, proper motions and parallaxes (thereby distances and 3D velocities).

2) determine 3D orbit family of the objects (circular, radial/very elongated, x2).

3) get statistics of the variability of the SiO maser features over a timescale of a year.

In principle, these goals will be achieved by determining positions of individual maser spots, and their motion across the sky. At 43 GHz the VLBA resolution is 0.17 mas, and the accuracy of the maser positions will depend on the angular separation from the calibrator, the atmospheric stability and the signal-to-noise ratio. While the formal errors on maser positions measured using 22 GHz H2O masers can be as small as 10-20 microarcsec, error terms of the order of 50 microarcsec are common due to, e.g., limitations of tropospheric calibration and accuracy of calibrator positions. Even though the SiO maser is at a higher frequency, it is therefore reasonable to assume similar error term sizes. An example of successful SiO maser parallax studies is the VERA result on R Aqr (d = 220pc; Min et al. 2014, PASJ, 66, 38). Our targets are further away, thus better represented by the VLBA observations of SiO masers near the Galactic Center, where maser positions were determined to an accuracy of 1 mas using the five inner antennas (Reid et al. 2003, ApJ, 587, 288). At the largest distances, where parallax distances may not be measurable, we are still sensitive to proper motion measurements. At the distance of the Galactic Center, a 200 km/s circular orbit will result in a yearly proper motion of 5 mas, whereas elongated orbits along our line-of-sight will show no observable proper motions. With the expected error budget we will be able to assign most individual targets with proper motions, and to distinguish orbit families (circular, elongated, etc.)

VLBA targets will preferentially be selected up to 40 degrees of longitude covering the full bar region. With the VLBA observations we are attempting to address the key sources selected from the VLA survey, to obtain better insight into the bar and bulge orbits. Therefore, we will also select targets at the end positions of the proposed long bar, targets with particularly high velocities, and so on. A very long-term goal is to follow a subsample of VLBA sources over more than 10 years, determining individual stellar Galactic orbits. With the 3D motions we may be able to say something about the orbit family. 3D motions will significantly improve the modeling of the Galactic dynamics and clarify, e.g., deviating kinematics in the interaction regions of the major components. Nearby bright masers can also be studied for detailed structure in their circumstellar envelopes. An additional outcome of the VLBI parallax studies is a detailed insight into the maser variability (periodicity etc.).

3.1 VLBA Observing and Calibration strategy and challenges

The calibration strategy in our VLA observations uses self-calibration of the masers, resulting in loss of the absolute position. The initial positional accuracy of our targets is therefore 1.5-2"" (MSX) but can be improved to less than 0.1"" by cross-matching using 2MASS source cross-matches (Pihlstrom et al., 2018 in prep.). This will save us much observing time, likely preventing intermediate steps of phase referencing the selected targets with the VLA in A-array first.

A major challenge for astrometry at 43 GHz is the availability of sufficiently nearby calibrators. Astrometric accuracy can be significantly improved by the addition of in-beam calibrators (e.g., Fomalont et al. 1999, ApJ, 512, L121; Vlemmings & van Langevelde 2007, A&A, 472, 547), that may be fainter than the primary calibrator. While there exists VLBI calibrator lists, filtering for sufficiently bright calibrators (at frequencies >20 GHz) located in the Plane quickly reduces the list to less than a handful. We have therefore begun testing new calibrators using VLA and VLBA. Although VLASS, GLOSTAR, BUTS and other partial VLA surveys of the Plane may be good starting points for finding additional candidate calibrators, experience tells us that dedicated VLA+VLBA X and/or Q-band follow-up will be necessary. Perhaps future surveys proposed for in this call for EoIs will allow a better initial selection (the GUTS survey; Sjouwerman et al.). In addition to the maser observations, we thus anticipate about 100h of VLA calibrator observations.

Once calibrators are selected, phase referencing will be applied to calibrators separated less than 1.5 degrees from the targets. The coherence time at 43 GHz is 30 seconds or less (Wrobel et al. 2000, VLBA Sci. Memo 24), in practice meaning that reverse phase referencing, using phase corrections of the maser spots to calibrate the calibrator, must be applied to many of our targets. Both imaging and non-imaging techniques (based on Bayesian inference) will be explored to derive positions of the masers. Geodetic blocks will be included to correct for tropospheric effects, which improves the phase stability considerably (e.g., Reid et al. 2009, ApJ, 693, 397; Sanna et al. 2014, ApJ, 781, 108). With three 30-minute geodetic blocks, and approximately 5x20 minutes phase-referencing observations per target (necessary for a well shaped synthesized beam), and including time on fringe finders and bandpass calibrators, we estimate about 2.25-2.5h per session per target (which will be revised marginally depending on how may targets per session we can observe).

Measuring positions is best done using the same maser feature through all epochs, which may not be possible due to variability. Individual maser features tend to be persistent through the stellar period, but not between cycles. In nearby objects like R Aqr (Min et al. 2014, PASJ, 66, 38) and OH44.8-2.3 (d=1kpc; Amiri et al. 2012 ApJ, 538, 136), individual maser features can be tracked. However, objects like R Aqr and TX Cam show a complex maser structure including internal motions with respect to the central star not easily modeled as a simple, linear motion expected from a stellar wind, but instead arising from partly bipolar structures (Gonidakis et al. 2013, MNRAS, 433, 3133). Where we cannot follow individual maser spots on linear trajectories, we will have to rely on estimating the stellar position from each epoch of the maser distributions. At our target distances, variations across the shell will most likely be blended, resulting in a stellar position uncertainty of at most the size of the shell (1 mas at the distance of the Galactic Center). Statistically we should be able to track the stellar positions, but it may require more, closer spaced epochs than just those needed directly for parallax and proper motion, thus we will aim for 6 epochs per target.

3.2 Spectral setup

We can cover both the SiO v=1 and v=2 (J=1-0) transitions at rest frequencies of 43.122 and 42.821 GHz respectively, using two dual polarization 512 MHz IFs centered between the two lines. The maser velocities are known from the VLA observations, and even though the masers are narrow (5-10 km/s) we will prefer to observe with two 64 MHz bandwidth channels across each line to achieve as good sensitivity as possible for calibration. With this bandwidth split into 1024 spectral channels we assure a high velocity resolution close to 0.4 km/s. This resolution will be useful in the imaging process, in case the lines consist of several different velocity components. The positional accuracy of our targets will be 0"".1 at worst, and an integration time of 1 second allows a conservative 1.5"" field of view, and also limits the data rate to be less than 5 Mbps. Across a 1 km/s channel with about 40 minutes on-source target time we expect to achieve an rms noise of about 7 mJy/bm. The target masers will all exceed 0.1 Jy, and our observations will not be sensitivity limited.

3.3 Comparison to the BeSSeL project

The VLBA excels of course at measuring the three-dimensional locations and motions of high-mass star forming regions in the Galaxy, using astrometric motions of methanol and water masers occurring in these regions (the BeSSeL project, led by Reid, CfA). We note that the proposed VLBI follow-up of our evolved stars survey will be complementary to the BeSSeL project in an interesting way, since we will be using a mixed sample of stars of different populations and mainly target the bulge while the BeSSeL project is aiming to derive the spiral structure in the disk of the Galaxy using star-forming regions. Furthermore, where the water and methanol masers provide detailed insight into the kinematics of stellar birthplaces, the SiO masers represent the more dynamically relaxed tracers of the gravitational potential. The recent findings by Reid et al. (2014, ApJ, 783, 130) considering the fundamental parameters of the rotation of our Galaxy can eventually be checked independently by BAaDE, which will be different as its targets are not associated with the kinematics of the spiral pattern.

3.4 Gaia versus VLBA parallax distances

The Gaia satellite will measure stellar parallaxes and proper motions for a stellar population similar to the one addressed by BAaDE, reaching far into the Galaxy, but with a limited view on the bar, due to interstellar extinction. However, it is of great interest to compare and cross-correlate our results with new findings on evolved stars by the Gaia mission. Initial results from DR2 shows about 2,200 of our targets have Gaia parallaxes sufficiently good to determine distances for (Quiroga-Nunez et al. 2018, IAUS, 336, 184). All of those are within 4 kpc, and while there are likely to be more BAaDE sources found in Gaia (we expect up to 30% from preliminary cross-matching), it is unlikely that there will be many BAaDE sources with Gaia distances beyond 4 kpc or in the obscured regions near the Plane. This is due to the combination of their, by nature, extended circumstellar envelopes and the large amount of extinction. Our infrared
selected evolved stars have obscuration provided both both by the envelope as well from the dusty material in the Galactic Plane, making Gaia G-band astrometry very difficult.","- There are no special technical resources required for the project, as the spectral set up, correlation and data reduction techniques are already existing.

- With the large amount of data expected, resources such as providing a work space at NRAO Socorro for 1-2 postdocs would be highly beneficial.

- The success of the proposed astrometry strongly depends on the availability of high frequency VLBI calibrators in the plane. Additional observing time at X-band and Q-band at the VLA to confirm calibrators is crucial (about 100 VLA hours A-array). The 3,500 hours suggested for the VLBA part includes 100 hours VLBA calibrator time.","Information for a large set of orbits will provide a much more secure conclusion to be drawn regarding the dynamical structure in the Bulge and the Bar. With only a handful of sources patters cannot be discerned. Having a commitment from NRAO to perform a 3,500 hours project without the need for small incremental time requests is thus imperative. Given the necessity to consolidate the calibrator list and allocate dedicated observing time to it also make such a program much less attractive to regular SRPs and usually end up at the bottom of the priority range. By committing to calibrator searches as required part of an X-proposal this section of the program will be secured."
Anatomy of Protostellar Jets,c.carrasco@irya.unam.mx,Carlos Carrasco-Gonzalez,"Guillem Anglada, Rachael Ainsworth, Esteban Araya, Crystal Brogan, Claire Chandler, Roberto Galvan-Madrid, Adam Ginsburg, Jose L. Gomez, Ciriaco Goddi, Melvin Hoare, Peter Hofner, Chat Hull, Todd Hunter, Katharine Johnston, Stan Kurtz, Hauyu B. Liu, Laurent Loinard, Stuart Lumsden, Enrique Macias, Karl Menten, Shane O'Sullivan, Willice Obonyo, Aina Palau, Alice Pasetto, Simon Purser, Tom Ray, Luis F. Rodriguez, Adriana Rodriguez-Kamenetzky, Viviana Rosero, Alberto Sanna, Jose M. Torrelles",2000,0,0,"The VLA has been a fundamental resource in the study of protostellar jets since the early 1990s. After the 2010's expansion, we have been applying all the new capabilities of the VLA to the star-formation context through several observational programs. Based on recent years experience, we have designed an observational project dedicated to answer specific still-open questions about protostellar jets. We will observe a sample of ~20 well known protostellar jets of different masses. We will perform very sensitive observations at several bands (C, X, U, K, Ka and Q) and different configuration to simultaneously detect the continuum and several lines (masers, ammonia and hydrogen recombination lines). We will observe jets and their environment at different scales, from a few AU to several hundreds of AU. Thus, we will study the regions where the material is launched and collimated into jets. Multi-epoch observations will provide variability and kinematic information, and linear polarization will allow to study the role of the magnetic fields in the jet collimation. The data and results from this project promise a lasting community legacy value.","Jets are present in a variety of astrophysical contexts. Although driven by very different objects (including supermassive and stellar-mass black holes and young and evolved stars), all jets share common characteristics, like their bipolar collimated morphology. Therefore, the jet phenomenon seems to play a universal role in the evolution of very different astrophysical objects. However, we still do not know which is (are) the mechanism(s) that launches and collimates the material into bipolar structures. Indeed, it is not yet clear if all kind of jets are governed by the same processes or if very different mechanisms could produce jets of similar appearance.

Among the different types of jets, the protostellar variety are usually considered as one of the less energetic manifestations. Because they appear at the earliest stages in the formation of a star and can extend up to several pc, jets likely play an important role in the evolution of protostars and protoclusters. It has been long believed that they regulate accretion onto the protostar by removing angular momentum from the circumstellar disk. Since the discovery of protostellar jets in the 1980s, several mechanisms have been proposed in order to explain their nature. The most commonly invoked can be described as ""self-collimation"" mechanisms, which consist of plasma confinement by a helical magnetic field generated in the disk/protostar system (e.g. Blandford+1982, Shu+1994). But, ""external-collimation"" mechanisms, where the plasma is collimated by the ambient medium pressure (e.g. Carrasco-Gonzalez+2015) or by a large scale ordered magnetic field (e.g. Albertazzi+2014), have also been proposed. It is also possible that different mechanisms dominate at different scales and/or different evolutionary stages of the central object (for reviews on different mechanisms, see Frank+2007, Shang+2007 and Pudritz+2007).

The VLA has been a fundamental resource in the study of protostellar jets since the early 1990s (e.g. Rodriguez1995). Radio emission at cm wavelengths in protostellar jets is dominated by free-free emission from shock ionized gas (Anglada+2018). Indeed, cm observations are the only way to trace the material of the jet near the protostar (within several hundred AU). More recently, the VLA also has enabled the detection of very weak areas of compact synchrotron emission in some protostellar jets, which implies the presence of relativistic particles in shocks within the jet (e.g. Rodriguez-Kamenetzky+2016). This discovery not only reveals new information about protostellar outflows, it establishes these jets as important nearby targets for the study of particle acceleration mechanisms (Ray2010). The presence of synchrotron emission also opens the possibility of measuring the magnetic field in these objects via linear polarization measurements, analogous to studies of magnetic fields in relativistic jets (Carrasco-Gonzalez+2010).

The spectacular increase in sensitivity of the VLA after 2010 offered the possibility of improving previous studies of protostellar jets in the radio domain. In particular, it made possible to detect and study emission from high-mass protostars, which are located at larger heliocentric distances (kpc) than low-mass protostars (hundreds of pc). We are now systematically detecting emission of the order of several microJy from high-mass protostellar jets, in a similar way we were detecting mJy emission in low-mass protostellar jets in the early 1990s (e.g. Rosero+2016). We now know that jets are also common at the earliest stages of the formation of massive stars. But, the increase in sensitivity also enables observations at higher angular resolution. Previous to 2010, it was extremely difficult to detect emission from jets at resolutions higher than 100 mas. Now, it is possible to reach resolutions as fine as ~30 mas by observing in the highest frequency VLA bands. Multi-epoch, multi-frequency and continuum+line studies are also now much more easy to perform, which spectacularly increase the amount of information obtained per observation time.

PROPOSED OBSERVATIONS

In recent years, all the people on this proposal have been involved in observational campaigns aimed at studying different aspects of the star formation process. Many of us have been using some of the new capabilities of the VLA to focus on specific aspects of the jet phenomenon via observational projects ranging from a few hours up to a couple of large programs. However, we feel that all the capabilities of the ""expanded"" VLA (EVLA) have not been yet fully exploited in this field. The new knowledge we can potentially obtain from future VLA observations is still huge in this field. But, we also feel that a big step in our understanding can only be achieved through a dedicated observational effort taking advantage of all the new capabilities of the VLA simultaneously, in a large sample of objects in order to obtain, not only results on individual objects, but especially general conclusions that help us to understand the jet phenomenon.

In order to study the jet phenomenon along the mass spectrum, we will select 15-20 objects covering a wide range in luminosities, from very low-mass protostars to high-mass protostars. In past years, we have accumulated different types of VLA and EVLA observations of a large number of objects, which will allow us to construct a good target sample. We will trace the jet material at several scales, from only a few AU to several hundreds of AU. It is in this region where launching and collimation of the jet takes place. We will also observe polarization to study the magnetic field configuration, and very deep integrations of molecular lines with very high angular resolution to study the physical conditions in the immediate environment of the protostar and the jet.

- Very deep A conf observations at K, Ka, and Q bands. These observations will provide a picture of jets and their environments with unprecedented high angular resolution (30-50 mas). We will observe continuum simultaneously with several lines in these bands. We plan to use around 100 hours per object obtaining continuum rms noises of the order of ~1-2 microJ/beam at each band. In these bands we also find water maser lines tracing shocks, ammonia lines tracing the physical conditions of the molecular gas, and recombination lines tracing kinematics of the ionized gas.

- Multi-epoch A conf observations at C, X, and U bands. These bands provide high sensitivity in very short observation times (~3 microJy/beam in ~1h), making multi-epoch studies very profitable. We plan to observe all objects in the sample at 4 epochs, spending ~5 h per object/epoch. These observations will trace the jet material at intermediate scales (from some tens to some hundreds of AU). Moreover, the multi-epoch and multi-frequency nature of the observations allow studies of variability, proper motions and changes in the physical conditions and/or emission mechanisms.

- Deep observations at C and X bands in C and B configurations. These observations are sensitive to scales larger than hundreds of AU. Over the years, we have identified several objects which show radio emission at these very large scales. We plan to observe a sub-sample with 30 h per object/band, probably the best ~5 objects. From these observations, we can study collimation at large scales, the terminal shocks of the jets, and large-scale magnetic fields through polarization.

*** WHAT WILL WE LEARN ***

This project will produce a comprehensive set of high quality data for a significant number of objects. While the analysis of these data will produce interesting results in several aspects of the star-formation process, the observations have been explicitly designed to answer four specific questions about how protostellar jets are launched and collimated.

* At what distance are jets collimated?

The distance from the protostar at which the material collimates into a jet is directly associated to the launching and collimation mechanisms. ""Self-collimation"" models predict that the material is launched from the accretion disk and it is already well collimated at distances of only 1-10 AU (Frank+2007). ""External collimation"" models assume that an initially poorly collimated wind is collimated at distances of the order of 100 AU (Albertazzi+2014). It is possible that the launching mechanism changes with the mass and/or the evolutionary stage of the protostar (Hoare2015), or that different mechanisms dominate the collimation at different scales. At present, the only answer we can give to this question is that protostellar jets seem to be already collimated at distances of hundreds of AU (Anglada2018), which is consistent with any model.

The angular resolution of the K, Ka and Q bands observations translate to physical resolutions of <10 AU at 150 pc (typical distances to low-mass star-forming regions), <20 AU at 400 pc (intermediate-mass regions), and <100 AU up to 2 kpc (high-mass regions). Thus, it is likely that we will resolve the collimation zone in some of the nearer objects. In the other objects, we will obtain the best size constraints to date. But even in these cases, by combining all the high angular resolution observations at all the bands, we can still obtain estimates of the collimation distance from the spectral energy distribution.

* What is the velocity of protostellar jets?

The velocity at which the material is injected into the jet is also an important parameter. We usually refer to the classical value of 100-200 km/s for the velocity of the jets. However, these values are actually based on measurements of proper motions of Herbig-Haro (HH) objects from optical observations of some low-mass jets. But, HH objects are shocks where the outflowing material actually brakes and they are located at distances of several parsecs from the protostar where the conditions of the ambient medium are very different. At the moment, it is also unclear if the material in high-mass protostellar jets is launched at similar velocities as low-mass protostars, or if they are much faster.

A much more representative value of the jet velocity can be obtained from proper motions of internal shocks near the protostar. At resolutions of ~100-500 mas, internal shocks are detected as bright compact radio knots embedded in diffuse emission from the jet. Their movement after a few years trace the actual velocity of the outflowing material in the jet. These kinds of observations have been made in a few protostellar jets and high velocities of 500-1000 km/s were found for the best studied cases (Marti+1995, Curiel+2006).

Kinematic information can also been extracted from hydrogen recombination lines. These lines are extremely difficult to detect in protostellar jets due their predicted weakness (Anglada2018). However, these will be the highest sensitivity observations ever performed on a large sample of jets, and we can combine a large number of lines in several bands. Thus, this program will provide our best opportunity to detect these lines in some objects.

* What is the role of the magnetic field?

Magnetic fields have a fundamental role in launching and collimation of the jet. Different models assume different configurations of the magnetic field (e.g., helical or large-scale ordered). However, observations of the magnetic field in star-forming regions are extremely difficult, and when it has been possible, they usually trace the magnetic field in the molecular material surrounding the jet, not in the jet itself (see Hull+2018). The detection of synchrotron emission in some protostellar radio jets opens the possibility of studying the magnetic field that the particles in the jet actually feel (Carrasco-Gonzalez+2010). For this, it is necessary detect linear polarization at several wavelengths where the synchrotron emission is important (C and X bands). Also, we should be able to study large scales, but with enough angular resolution.

These studies are extremely difficult to perform since we need to detect very weak polarized emission, but we cannot obtain high sensitivity by simply averaging large bandwidths because of large depolarization effects due to the expected large Faraday Rotation. Therefore, we still need very long integrations. The advantage now is that in a single long integration, we can obtain polarization at several wavelengths within the band, making this study possible in, at least, a handful of objects.

* What is the role of the ambient medium?

The ambient medium could also play an important role in the collimation of the jets. There is evidence of re-collimation at large distances from the protostar in some objects (e.g. Rodriguez-Kamanetzky+2017). Self-collimation could be responsible for the initial collimation of the jet, but external collimation could be also necessary to maintain the jet confinement at larger scales (see Frank+07). Some models propose that external collimation by the environment is the only possible mechanism to collimate the jet even at distances of only several hundreds of AU (Albertazzi+2014). Our sensitive high angular resolution continuum+line at K and Ka bands, and the C and X bands at different configurations, will allow us to simultaneously study the physical conditions in the ambient medium (through ammonia lines), shocks (water masers), and the ionized gas (continuum), all at very different scales (from tens to hundreds of AU). We can then compare changes in the collimation degree of the jet with the physical conditions in the ambient medium in order to understand what is the collimation mechanism.

REFERENCES

Albertazzi et al. 2014, Science, 346, 325
Anglada, Rodriguez, Carrasco-Gonzalez 2018, A&ARv, 26, 3
Blandford & Payne 1982, MNRAS, 199, 883
Carrasco-Gonzalez, Torrelles et al. 2010, Science
Carrasco-Gonzalez, Rodriguez et al. 2015, Science
Curiel et al. 2006, ApJ, 638, 878
Frank et al. 2007 in Protostars and Planets VI
Hoare 2015, Science, 348, 44
Marti et al. 1995, ApJ, 449, 184
Pudritz et al. 2007 in Protostars and Planets VI
Shang et al. 2007 in Protostars and Planets VI
Shu et al. 1994, ApJ, 429, 781
Ray 2010, Science, 330, 1184
Rodriguez 1995, RMxAC, 1, 1
Rodriguez-Kamenetzky, Carrasco-Gonzalez et al. 2016, ApJ, 818, 27
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Rosero, Hofner et al. 2016, ApJS, 227, 25","This project will produce a huge amount of data of different nature: continuum, lines, polarization, multi-frequency, multi-epoch data. In principle, we expect to use standard observing modes, thus, no special resources will be required. Data reduction may be conducted in parallel among the different institutions in this collaboration. Many of the members in this collaboration count with laboratories equipped with multi-core workstations and several hundreds of TB harddrive space for data reduction.

However, we do anticipate that we will also need to closely work with personal from the NRAO to solve problems related to observational strategies, calibration techniques (specially pipelines), imaging, etc. It may be necessary also to make use make use of NRAO's computing resources, including CPU and disk space requirements. It is possible that a centralized NRAO website and archive space be requested to make the final data products available to the community.

The kind of data that will be generated by this project will be excellent to test new calibration, imaging and analysis techniques which are currently being developed by the NRAO. We hope we can closely work with the NRAO's staff in order to obtain the best information from our data by using these new techniques.

The data produced by this project will be also very useful for other scientific objectives apart of the main objectives discussed here. For this reason, we think that it would be extremely useful to made them available to the public. Then, we expect to work with the observatory in exploring which are the best products to be offered and which are the best ways to make them available.

Multi-epoch observations may require in some cases of fixed dates for the observation, or at least to guarantee observation within a range of dates.","A significant fraction of the star formation community represented by the coauthors of this Expression of Interest (EoI) proposal has realized that a thorough understanding of the role of protostellar jets can be achieved by consolidating efforts in a major VLA project. Given the ambitious scientific goals listed below, which require 1000+ hours, this project is ideal for an eXtra-large VLA proposal and cannot be achieved through the standard SRP/TAC process due to the need of continuity in muti-frequency, multi-configuration and multi-epoch observations. The data and results from this project promise a lasting community legacy value."
J-BooDeeS: the JVLA Bootes Deep Survey,rev@voo.it,Francesco de Gasperin,"R.J. van Weeren, H.J.A. Rottgering, S. Alberts, P. Arras, R. Battye, P.N. Best, M. Brienza, M. Brodwin, M. Brown, M. Bruggen, G. Calistro-Rivera, J.R. Callingham, K.T. Chyzy, R.K. Cochrane, V. Cuciti, G. Di Gennaro, K.J. Duncan, K.L. Emig, T.E. Ensslin, A. Gonzales, G. Gurkan, I. Harrison, J.J. Harwood, V. Heesen, R.C. Hickox, D.N. Hoang, J. Hodge, M. Hoeft, C. Horellou, H.T. Intema, C.H. Ishwara-Chandra, N. Jackson, B. Jannuzi, R. Kale, K.-S. Lee, M. Kunert-Bajraszewska, V. Mahatma, S. Mandal, G. Miley, B. Mingo, S. O'Sullivan, A. Pope, I. Prandoni, E. Retana-Montenegro, J. Sabater, A. Saxena, S. Sekhar, T.W. Shimwell, A. Stanford, C. Tasse, V. Vacca, D. Vir Lal, G.J. White, A. Wilber, W.L. Williams",1560,0,0,"Galaxies that populate the local Universe are morphologically and chemically diverse. The activity in their nuclei, combined with the formation of galaxy groups and clusters, seems to have shaped a significant part of their evolution. The nature of this evolutionary process is a major question in modern astronomy, which can be addressed by multi-wavelength observations of large fields. However, radio observations have thus far lagged behind other wavelengths when combining area coverage and sensitivity. We will use the combined effort of JVLA, uGMRT and LOFAR to fill this gap, with a relatively modest time investment from each of the facilities.

We propose to make the first deep survey of a large field with the JLVA. This survey will cover the Bootes field (9 sq deg) down to a sensitivity of 3 uJy/b in L-band, and will overlap the LOFAR Bootes Deep Survey (L-BooDeeS) and the GMRT Bootes Deep Survey (G-BooDeeS). The combination of these surveys will create a data set that will be unique even into the SKA era. The Bootes field has wealth of ancillary data, including spectroscopic information (with new WEAVE data coming), deep infrared surveys, and mega-second X-ray observations.","The BooDeeS project is based on the synergy between its surveys. Preliminary L-BooDeeS data showed that we can reach an rms noise of 20 uJy/b at 150 MHz across the Bootes field, while the planned G-BooDeeS survey will reach 10 uJy/b at 400 MHz. These three surveys were designed to have similar sensitivity for average spectral-index sources (-0.8), which combined with the large spread in frequency, will provide an unique radio SED collection (including curvature), covering the majority of the detections. The combination of these surveys will also offer increased reliability in the detection of faint sources by confirming multiple low-level detections. The projects are highly complementary: the resolution of J-BooDeeS will be fundamental to unambiguously identify optical counterparts, distinguish the morphology of distant objects, and extract polarisation information; conversely, G-BooDeeS and L-BooDeeS will provide strong constraints to extended and aged emission, as well as providing critical spectral information.
The proposed survey area is sufficiently large to ensure that low number statistics do not bias the results, and will allows an assessment of galaxy properties as a function of different large-scale environments (clusters, filaments and voids). Current samples at similar depths cover more modest areas; e.g., the COSMOS survey covers 2 sq deg, corresponding to just about 40 Mpc at z>1 (Smolcic+ 2017 A&A 602 6).
The composition of the radio population changes as a function of frequency, flux density and redshift, with the fraction of flat-spectrum sources increasing dramatically with decreasing flux density (de Gasperin+ 2017 MNRAS 467 2234). At GHz frequencies, bright steep-spectrum sources are dominated by evolved radio galaxies, whereas flat-spectrum sub-mJy sources are more usually related to AGN cores, and at flux densities below 200 uJy, star-forming galaxies appear to become the dominant population. Due to their spectral properties, faint sources cannot be well studied at low frequencies (LOFAR, uGMRT), and the proposed depth of J-BooDeeS is required to sample the luminosity function of both AGN-powered radio sources and of the star-forming galaxy population, across comic time ranging from the reionisation epoch to the present day.
* The Bootes field
The Bootes field is arguably the best studied large-area extragalactic field, with ancillary multi-wavelength observations covering enough of the area to meet our survey criteria. Besides the deep LOFAR 150 MHz and uGMRT 400 MHz surveys outlined above, radio observations have also been carried out at 153 MHz with the GMRT (2 mJy/b; Williams+ 2013 A&A 549 55), at 325 MHz with the VLA (200 uJy/b; Coppejans+ 2015 MNRAS 450 1477) and at 1.4 GHz with the WSRT (28 uJy/b; de Vries+ 2002 AJ 123 1784). The field has also been observed with the LOFAR at 50 MHz (5 mJy/b; van Weeren+ 2014 ApJ 793 82), with deeper observations down to 100 uJy/b scheduled.
The Bootes field is part of the NOAO Deep Wide Field Survey (Jannuzi+ 1999 ASPC 191 111) covering 9 sq deg in the optical and near-infrared bands. It is also covered by PanSTARRS and observed with SuprimeCam. The AGN and Galaxy Evolution Survey has provided redshifts for 23,745 galaxies and AGN (Kochanek+ 2012 ApJS 200 8). Most important, WEAVE-LOFAR will provide spectroscopy for ~5500 sources per sq deg, selected down to ~100 uJy/b at 150 MHz. These will provide precise redshifts, and allow robust source classifications by cleanly separating different radio source types. The field has also been covered by X-ray (Murray+ 2005 ApJS 161 1), UV (GALEX), and mid- and far-infrared observations (Spitzer/Deep Wide-Field Survey and Herschel/HerMES respectively). Broadband SED fitting will be used to provide robust host galaxy parameters such as photometric redshifts, stellar masses, and star formation rates.
* Galaxy evolution and star-formation
The star-formation rate (SFR) density rises as a function of redshift out to z~1-2 and then flattens (Lilly+ 1996 ApJ 460 1L). As a result, the bulk of stars present today were formed in the range z=1-3. However, different indicators give largely different measurements of the SFR density (e.g. Hopkins & Beacom 2006 ApJ 651 142), which together with the small sample size of the available surveys, leave large uncertainties about the cosmic star formation history.
The radio emission from star-forming galaxies offers a reliable SFR indicator across the entire history of the Universe. The depth of the proposed survey is sufficient to detect galaxies forming stars at a rate of 10 Msun/yr at z~1 and 50 Msun/yr at z~2 (Brown+ 2017 ApJ 847 136). More importantly, the radio continuum is immune to dust extinction, and is able to identify heavily obscured systems missed in optically selected samples. The combination with infrared data will allow us to track the evolution of the radio-FIR relationship across cosmic time. Finally, multi-frequency radio data will enable k-corrections and reduce uncertainties in the SFR estimation and can provide independent estimators for systems where both star formation and AGN activity are occurring, allowing us to better disentangle both contributions. Beside the global SFR history, further key questions that will be addressed in this study include:
What is the relation between the SFR and the galaxy mass? What is the role of the environment? In the local Universe, most massive galaxies have already formed the majority of their stars, which implies that they were formed before less massive ones (the so-called ""down-sizing""; e.g. Cowie+ 1996 AJ 112 839). At the same time, in the local Universe star formation is suppressed in over-dense environments (Rasmussen+ 2012 ApJ 757 122), this effect seems to diminish at higher redshifts (Ziparo+ 2014 MNRAS 437 458). It is unclear when this environmental effect becomes important, and how to disentangle the competing effects of environment and stellar mass in quenching star formation.
What is the relationship between AGN activity and star formation? The cosmic SFR rate closely mirrors the cosmic accretion rate onto AGN (Croom+ 2009 MNRAS 399 1755), while AGN activity seems vital to reproduce the observed stellar mass functions (Croton+ 2006 MNRAS 365 11) and the black hole mass versus bulge velocity dispersion correlation (e.g. Robertson+ 2005 ApJ 641 1). It is also known that (radio-loud) AGN activity can be responsible for a shutdown of the star formation in massive galaxies. However, a clear identification of such a link has remained elusive at higher redshifts, although evidence of positive feedback, where the AGN activity enhances star-formation has been predicted theoretically (Silk 2013 ApJ 772 112), and claimed observationally (Kalfountzou+ 2012 MNRAS 427 2401). Different forms of AGN feedback have been invoked in semi-analytic models of galaxy formation, but they need to be better understood.
J-BooDeeS will address these questions without limitations due to cosmic variance. We aim to have reliable (5 sigma) detections of >8,000 galaxies in each of the redshift bins [0-0.5, 0.5-1, 1-1.5, 1.5-2, 2-3], and >4,000 detections above a redshift of 3. The optical counterparts and the large multi-wavelength coverage will provide spectroscopic or excellent photometric redshift estimation, together with other information such as mass, environment and classification as AGN or merger.
* AGN accretion and feedback
AGN activity can be divided into two fundamental modes (Hardcastle+ 2007 MNRAS 376 1849; Best & Heckman 2012 MNRAS 421 1569). Accretion at high Eddington (> 1%) rates produces radiatively efficient AGN (quasar or radiative mode), where much of the accretion energy may emerge as luminous radiation from the accretion disk. By contrast, accretion at low Eddington rates produces radiatively inefficient AGN (radio or kinetic mode) in which almost all of the energetic output is carried by the radio jets. Both classes of AGN are thought to have significant, but different effects, on host galaxy evolution. However, many fundamental questions remain open:
What are the relative importance of jet- and radiative-mode AGN activity? How does this evolve across cosmic time? The role of the two accretion modes seems to be influenced by the environment (Tasse+ 2008 A&A 490 893) and the stellar mass of the host galaxy (Janssen+ 2012 A&A 541 62). J-BooDeeS will sample both classical radio-loud AGN and the elusive radio-quiet AGN between z=0-6. The cosmological evolution of this relationship is fundamental to the incorporation of mechanical feedback of radio-loud AGN into models of galaxy and cluster formation. J-BooDeeS' spatial resolution will be necessary to distinguish jet phenomena from the star-formation emission, and will provide a complete view on galaxy nuclear activity free from gas/dust selection effects.
How is the energy produced by AGN transferred to the surrounding gas? Basic aspects of AGN-environment interaction, in particular whether the lobes of powerful sources are expanding supersonically, or what provides their pressure support, remain unclear (Hardcastle & Worrall 2000 MNRAS 319 562). These questions can be answered only from large and statistically complete samples, where both the core AGN activity (from J-BooDeeS) and the extended lobe emission (from L-BooDeeS) can be measured.
When are the first black holes formed? Can we use them to study the primordial Universe? High-redshift radio galaxies trace the most massive galaxies, host the most massive black holes, and also mark the locations of the most over-dense regions (Kuiper+ 2012 MNRAS 425 801), and as such are key to understanding galaxy and supermassive black hole formation at high redshift. The combination of the BooDeeS surveys will be unique to identify the presence of very steep-spectrum sources that have been shown to effectively trace radio galaxies at high redshifts. Additionally, the high resolution of J-BooDeeS will facilitate blind follow-up spectroscopy of radio sources that do not have optical or infrared counterparts, which is also an efficient and unbiased method of pin-pointing high-redshift sources (Ker+ 2012 MNRAS 420 2644). There still remains the big challenge of detecting a radio galaxy deep in the epoch of reionisation (z>6) and down to the proposed BooDeeS depths, and we expect to detect ~20 radio galaxies at z>6 in this survey (Saxena+ 2017 MNRAS 469 4083).
* Radio galaxies
The BooTeeS spectral data will show with unprecedented statistical accuracy the way radio galaxies are born, evolve, fade and interact with the surrounding medium. Spectral curvature will be used to detect compact steep-spectrum sources (CSS) and gigahertz-peaked spectrum sources (GPS), both classes are thought to be the young precursors of large-scale radio galaxies (O’Dea 1998 PASP 110 493). The BooDeeS surveys will allow us to probe a significantly fainter population of peaked-spectrum sources than previously possible (Callingham+ 2017 ApJ 836 174). Such a data set will be invaluable to assess the evolutionary scheme of young radio sources.
In addition, the BooDeeS project will assemble the largest sample (by an order of magnitude) of FRI/II radio galaxies for which we can obtain tight constraints to the spectral curvature on well resolved scales. J-BooDeeS will be necessary to determine the cut-off frequency, and to provide vital information on the low-energy particle population and source ages, for both compact and diffuse structures. This will allow, for the first time, an empirical determination (Harwood+ in prep) of the energetics of a statistically significant sample of radio galaxies. This, in turn, is a critical component in understanding the wider impact of AGN on the surrounding medium, and on galaxy evolution as a whole.
AGN activity is a recurring phenomenon, however the number of known remnant radio galaxies are less than expected when selected using shallow surveys (Brienza+ 2017 A&A 606 98). The combined BooDeeS surveys will enable the first census of remnant radio galaxies. At the same time, J-BooDeeS resolution and sensitivity will enable an investigation of the AGN core activity in these sources (Mahatma+ 2018 MNRAS 475 4557). All this will be necessary to understand AGN duty cycle, with far-reaching implications for AGN feedback, formation of SMBHs, and triggering of radio jets.
* Cosmic magnetism
Radio galaxies show high degrees of polarisation, up to 30% for radio-loud QSO, and different magnetic properties depending on their accretion mode (O'Sullivan+ 2015 ApJ 806 1). With J-BooDeeS we will detect polarisation from radio galaxies up to high redshift, pin down their properties with respect to the host galaxy characteristics, and map the evolution of polarisation and Faraday rotation, and hence the magnetic fields, across cosmic time. A fractional polarisation higher than 1% (up to 10% in certain cases) has been measured also in 60% of nearby disk galaxies (Stil+ 2009 ApJ 693 1392). The proposed survey would assess the presence of ordered magnetic fields in galaxies up to z~1 through direct detection or using rotation measures (RM) of background sources (Farnes+ 2014 ApJ 795 63). Radio polarisation properties will be correlated with SFR, emission lines and galaxy type, to help clarify whether magnetic fields are important in controlling star formation in spiral galaxies (Basu+ 2017 MNRAS 471 337).
The detection of extragalactic magnetic fields is still challenging. J-BooDeeS will produce a dense RM grid (~50 per sq deg; Rudnick & Owen 2014 ApJ 785 45) tracing the weak magnetic fields along clusters and filaments of the large-scale structures, predicted to have an RM signature ~>1 rad/m2 (Vazza+ 2017 CQGra 34 234001). The Galactic foreground will be isolated by statistical arguments exploiting consistency of the Galactic Faraday rotation map (Oppermann+ 2012 A&A 542 93O) combined with cross-correlations of the extragalactic signal with multi-wavelength data (e.g. Vernstrom+ 2017 MNRAS 467 4914) and tracers of the cosmic large-scale structure (Vacca+ 2016 A&A 591 13).
* Transients
The long time-base of the observations for the survey will usefully allow us to study transient events. AGN will be monitored to find both slow and fast time-variability. Some of the variability changes can be manifestation of the ignition of radio activity (Mooley+ 2016 ApJ 818 10). Thus, the proposed multi-epoch survey will provide an unique opportunity to study new-born, fast-evolving AGN jets.
* Weak lensing shear
The large number of sources over a wide area, together with relatively good resolution, should allow a detection of the cosmic weak lensing shear signal in the radio at about 4-5 sigma. Radio weak lensing is potentially very important, because of the reduction in systematics due to the well-controlled PSF compared to the optical and also by cross-correlating radio and optical shear maps (e.g. Patel+ 2010 MNRAS 401 2572).","We have assembled an international team of experts experienced both in the technical, and in the scientific sides, including astronomers/developers currently working on 3rd generation data reduction software for SKA. This will ensure a full exploitation of the data. We will ask the collaboration of the observatory to ensure proper scheduling of the observations across multiple cycles. Given the legacy value of the project, we plan to make the following products public shortly after each observing cycle: raw data, calibration tables, integrated images / image cubes (at different resolution) and source catalogues. We ask the observatory for the computing facilities to store and distribute these products. Data reduction would be ideally carried out at NRAO, however a number of external facilities (e.g. the Hamburg radio group cluster) are also available. At the end of the project we plan to make available to the community a number of high-level deliverables, including: full-stokes images, image cubes, RM cubes, source catalogues (including polarisation and RM), enhanced catalogues with multi-wavelength cross-matching and source classification.","As discussed in the scientific case, the coverage and depth of the survey are key points to achieve our goals. To reach 3 uJy/beam rms at 1500 MHz, we need 13 hours of JVLA observing time. Given the Bootes area of 9 sq degrees, we need a total of ~950 hrs on-source to reach that depth uniformly across the survey area. Calculations were based on the VLA mosaicking guide. Observations will be carried out in A, B, and C configurations to achieve the arc-second resolution while being sufficiently sensitive to extended emission. We will adopt a conservative approach by adding time for more compact configurations following: A:B:C = 1:1/4:1/16, i.e. A = 950 hrs, B = 240 hrs, C = 60 hrs for a total of 1250 hrs. Assuming a 25\% of overhead this gives a total of 1560 hours."
Resolving the radio sky with a VLBA wide-area legacy survey,mckean@astron.nl,John McKean,"J. Radcliffe (Co-PI; U. Man.), M. Argo (U. Lanc.), R. Beswick (U. Man.), P. Barthel (U. Gron.), S. Burke-Spolaor (Caltech), R. Deane (U. Pret.), A. Deller (U. Swin.), C. Fassnacht (UC Davis), J. Forbrich (U. Herts.), N. Herrera Ruiz (U. Boch.), M. Hoare (U. Leeds), M. Garrett (U. Man.), N. Gupta (IUCAA), P. Jagannathan (NRAO), E. Lenc (CSIRO), T. Maccarone (Texas Tech.), J. Morgan (U. Curtin), R. Morganti (ASTRON), T. Muxlow (U. Man.), S. Myers (NRAO), A. Readhead (Caltech), W. Rujopakarn (U. Chul.), F. Schinzel (NRAO), C. Spingola (U. Gron.), H. Stacey (U. Gron.), G. Taylor (U. New Mex.), M. Thompson (U. Herts.), A. Thomson (U. Man.), G. Tremblay (CfA), G. Umana (INAF), N. Wrigley (U. Man.), A. Zensus (MPIfR)",0,0,3500,"A new avenue for studying the Universe at the highest available angular resolutions in astronomy has recently been opened-up, allowing hundreds of objects to be observed simultaneously at high surface brightness sensitivity. Here, we present a two-component survey strategy with the VLBA that will uniquely reveal the nature of black hole formation, star-formation processes and dark matter physics, whilst providing a critical test of galaxy formation models. The first-tier is an all-sky survey with the VLBA at 1.4 GHz (3500 h) that matches the VLASS footprint (Dec. > —30 deg) down to a central rms of 0.14 mJy/beam, and is projected to detect over half a million radio sources at mas-scales. The second-tier uses the data from regular PI-led projects to map the radio source population within the primary beam of each observation, expanding sample sizes to lower flux-limits and higher frequencies. This overall survey strategy will have lasting legacy value, providing synergies with the next generation of synoptic surveys (LSST) and extremely large telescopes (TMT, GMT, ELT, JWST), whilst expanding and connecting the VLBI communities at mm (ALMA) and cm-wavelengths.","1. Introduction
It is over 50 years since the first fringes were produced between two un-connected antennas, yet the unique astrophysical applications of VLBI at cm-wavelengths have been restricted to studying only ~20000 radio sources with very high brightness temperatures and over a very small fraction of the observable sky (few hundred square degrees; Deller & Middelberg, 2014, AJ, 147, 14). However, we are now in an era where the number of objects detected on mas-scales can be increased by several orders of magnitude due to innovative methods for correlating the individual antennas. In particular, flexible techniques for multi-phase centre correlation now allow the full primary-beam of a VLBI experiment to be imaged (Deller et al., 2011, PASP, 123, 275) and multi-source self-calibration can be used to reach the thermal noise levels efficiently (Radcliffe et al., 2016, A&A, 587, A85). Here, we propose a survey strategy that will increase the number of radio sources with VLBI detections by over an order of magnitude. In this EoI, we present a community wide (working group of currently 33 astronomers from 9 countries) proposal for a two-component survey at mas-scales with the VLBA that aims to independently uncover the nature of dark matter and understand the physics of feedback from AGN, whilst delivering complimentary and comparable quality imaging of the non-thermal sky to what will be provided by the next generation of optical to mm-wavelength facilities. For example, the TMT, GMT, E-ELT and the JWST will provide 5 to 70 mas angular resolution imaging and spectroscopy of the thermal processes associated with AGN and star-formation activity, and ALMA currently provides imaging of the cold molecular Universe with a 10 to 75 mas smallest beam-size. Such synergies with multi-wavelength astronomy are important for developing and growing the VLBI community in the future.
2. Survey Outline
To achieve our science goals, we have devised a two-tier survey strategy that involves dedicated survey observations and commensurate observing with PI-led projects.
A wide-field survey with the VLBA: This survey will target up to 4 million radio sources detected by VLASS at Dec. > —30 deg, down to a sensitivity of 0.14 mJy/beam (central rms) at 1.4 GHz (5 to 15 mas beam-size). The primary aim is to discover rare types of radio-sources that can only be detected through wide-field and high angular-resolution observations, such as strong gravitational lenses, dual and binary AGN, unusual VLBI jet morphologies and young radio sources, whilst also providing a parent sample of sources to investigate mechanical feedback through cross-referencing with the all-sky and deep spectral line surveys for HI and OH. The choice of frequency, sensitivity and area is based on a preliminary analysis, given our primary science goals (see below for details). However, as a working group we are preparing comparative studies to determine the optimum survey strategy. The current plan is to have a survey with a footprint of 9.42 sr, about 155 times larger than that of mJIVE-20, but to a similar depth. Going significantly deeper will not result in many more detections due to the turnover in the radio source number counts as the population changes from AGN to star-formation dominated galaxies. This is expected to increase the number of radio sources detected on VLBI-scales at 1.4 GHz from around 5000 to >770000. To achieve this sensitivity will require 90 s per-pointing for a recording-rate of 4 Gbps at a central frequency of 1.4 GHz. This could also be achieved through 3 x 30 s pointings to obtain transient / proper motion information. To complete the survey will require around 118000 pointings, and a total of 3000 h on-source. The time required for calibration (~500 h) depends on the final observational strategy as phase-referencing will be achieved in-beam, and the amplitude calibration will be obtained from the antenna system temperatures.
Commensurate observing programme: In addition to the wide-area survey described above, it would also be advantageous to study the radio source population at intermediate depths, over an intermediate sky area and at higher radio frequencies. Such a survey could be carried out as part of a dedicated set of observations, requiring a similar observing time to the survey described above. However, given that PI-led programmes have typically 2 to 10 h on-source, by also correlating at the positions of VLASS/LOFAR/MeerKAT/ASKAP sources within the primary beam of these observations will allow the community to probe emission at the 15 to 30 uJy/beam level (assuming at least a 1 Gbps recording-rate). In addition, a commensurate observing programme will also provide information at other frequencies (and higher angular resolution). Such a dataset will be useful for improving image fidelity for a sub-sample of objects, whilst increasing the sample sizes available for our primary science goals, without the need for additional observing time.
3. Science Cases
Here, we give details on the specific science goals that can be achieved with the strategy described above. Note that we have focused on the high-impact and unique science applications that can only be achieved at mas-scales with the VLBA, but the legacy value of a wide-area survey will motivate further studies by the radio (and general) astronomical community.
3.1 Dark Matter: Uncovering the nature of dark matter is fundamental if we are to have any understanding of how our Universe formed and evolved. This can be done by measuring the dark matter (sub-)halo mass function, which has definite and different predictions for various models for both cold and warm dark matter (including baryonic effects; Bullock & Boylan-Kolchin, 2017, ARA&A, 55, 343). The most promising method for detecting and quantifying the abundance of low mass dark matter haloes (> 1 million solar masses) is through their gravitational lensing effect on various-scales (Vegetti et al., 2012, Nature, 481, 341). Based on the gravitational lensing rate from CLASS (Browne et al., 2003, MNRAS, 341, 13) and the number-counts of compact radio sources (McKean et al., 2007, MNRAS, 377, 430) we find that 1100 sources from the all-sky survey considered here will be gravitational lensed by massive foreground galaxies; a factor of over 30 higher than current samples. However, not all of these will be immediately discovered in the survey data alone as the weakest lensed images may not be detected. Based on the imaging sensitivity, we expect to detect a statistically complete sample of 120 gravitational lenses; an order of magnitude larger than CLASS. However, given the excellent angular resolution, we will likely find in total 340 new gravitational lenses (not statistically complete). Indeed, a pilot lens-search of the mJIVE—20 survey identified 2 gravitational lenses efficiently from a sample of 3640 radio sources, without the need for extensive followup (Spingola et al., 2018, MNRAS, in prep.). Finding the remaining 760 gravitationally lensed sources would require significant follow-up with the VLBA and the cross-correlation with optical catalogues (e.g. LSST) using novel matching techniques (Jackson & Browne, 2007, MNRAS, 374, 168), which is of interest in the long-term, but is not needed to successfully complete the main science goals.
This large sample of radio-loud lensed objects will be used for two main science goals.
Dark matter substructure mass function: Around 120 new four-image (compact images) galaxy-scale lenses (0.5 to 3 arcsec image separations) will be used to constrain the dark matter substructure mass-function via their flux-ratios (Dalal & Kochanek, 2002, ApJ, 572, 25). This sample size would improve current constraints by over an order of magnitude. Also, it has been recently estimated that 120 to 180 lensed four-image systems in total are needed to differentiate between cold and warm dark matter models (Gilman et al., 2018, MNRAS, in press). Also, new gravitational lenses with extended gravitational arcs will be identified for follow-up, placing limits on the abundance of million solar mass substructures within massive lensing galaxies (Spingola et al. 2018, MNRAS, 478, 4816). The direct detection of even a single low-mass substructure at this level would immediately rule out warm dark matter models (Despali et al., 2018, MNRAS, 475, 5424).
Dark matter halo mass function: Gravitational lenses with image separations in the 0.1 to 0.3 arcsec regime would be used to constrain the dark matter halo mass function for galaxies at the low-mass end. No gravitational lenses with image separations < 334 mas are known, as the lensing optical depth of low mass galaxies is so low. It is expected that around 5% of the gravitational lenses found from an all-sky survey will be in this new low-mass regime, given the predictions from cold dark matter models and the large parent sample size. In addition, the survey would also be sensitive to gravitational lenses with image separations in the 5 to 100 mas regime; here the lenses come from a rich population of low mass dark matter haloes or exotic objects like free-floating black holes throughout our Universe (Wilkinson et al., 2001, PhyRevL, 86, 584). Given the large parent sample size, the non-detection of any gravitational lenses in this >1 million solar mass regime would essentially rule out cold dark matter. Only the angular resolution of VLBI can detect such lenses
Overall, such a survey can revolutionise studies of dark matter through independently measuring the sub-structure mass-function within galaxies, whilst uniquely probing the low-mass end of the dark matter halo mass-function.
3.2 Black hole formation, accretion and feedback: The second primary science goal is to test hierarchical galaxy formation models and feedback on the scale of SMBHs at the centres of all massive galaxies, and search for stellar mass black holes within our Galaxy. This part of the survey will provide a parent sample for statistical studies of galaxy formation and accretion processes through the detection of over half a million objects, will motivate further observations with the VLBA/ngVLA and SKA-VLBI in the future, and provide synergies with the next generation of high resolution optical telescopes.
The individual science goals are as follows.
A new population of dual/binary SMBH systems: Determining the rate of dual AGN in galaxy mergers provides a direct measure of merger-induced activity, SMBH growth, and the physical processes that drive the dynamics and the in-spiral of black hole pairs (Kharb et al., 2017, Nature Ast., 1, 727). Such objects are also sources of cosmological gravitational wave events that are of interest to the next generation of space-based (GW) interferometers. Due to the expected fast in-fall, such systems are extremely rare to detect (Mayer et al., 2007, Science, 316, 1874), and so a wide-field VLBA survey can efficiently find new targets with > 40-pc separations at redshift 1, where the galaxy merger-rate was highest. Such candidates can be studied in detail with VLBI (VLBA and ALMA) and with optical ELTs to understand their dynamics and their effect on gas accretion. Finally, such a survey would also find extremely rare triple SMBHs and possibly more exotic systems (Deane et al., 2014, Nature, 7507, 57) given the sensitivity and excellent angular resolution.
AGN feedback and testing gas accretion with HI and OH absorbers/masers: The diffuse ISM exhibits a wide range of astrophysical conditions (temperature, density and radiation field) and structures up to kpc-scales in the form of shells, filaments and spurs. Understanding pc-scale HI opacity fluctuations in the ISM of galaxies and how they depend on the feedback from in-situ star formation and AGN activity is important for understanding galaxies and their evolution. Large area surveys with the VLA, MeerKAT, ASKAP and APERITIF will detect atomic and molecular gas in galaxies out to z < 2 at 6 to 15 arcsec angular resolution. More than 1000 absorbers associated with normal star-forming galaxies and AGN are expected, which can be used to trace the pc-scale structure in high-z galaxies when coupled with VLBI. An all-sky VLBA survey is important to derive the main science goals from these low resolution surveys; it will identify prime continuum targets for deep follow-up VLBI spectroscopic imaging to directly observe the gas physics on pc-scales and understand the fuelling of star-formation and AGN activity (Morganti et al., 2013, Science, 341, 1082), and also gas accretion (Klockner et al., 2003, Nature, 421, 821).
Young radio sources and testing the duty-cycle of AGN activity: Hydrodynamical models of galaxy formation require episodic outbursts from AGN to control the amount of gas available for star-formation (Vogelsberger et al., 2014, Nature, 509, 177). Testing this model statistically requires sampling a large number of galaxies over cosmic time that have evidence of aged, diffuse emission on large-scales and jet-emission on VLBI scales. The broad-band spectral information from the all-sky surveys provided by LOFAR/GMRT, MeerKAT/FIRST and VLASS will identify flat and inverted spectrum radio sources which when coupled with the morphological information provided by the VLBA will allow candidate young radio sources to be found. Follow-up imaging at higher angular resolutions will confirm that they are compact symmetric objects, possibly expanding over time. Synergies with ALMA and the ELT’s will trace the impact these triggered sources have on the gas accretion of the SMBH, and test models for mechanical feedback on pc-scales.
Stellar evolution: The all-sky survey will provide both a first epoch, and a calibrator survey, for proper motion and parallax measurements for stellar radio sources, including some that are not yet known. Among normal stars these sources may include strongly coronally active single stars, which can be used to test the precision of GAIA; coronally active binary stars, which can be used to do visual binary work in the radio (even with separations smaller than provided by GAIA), allowing precision mass measurements that can be used to test theories of stellar evolution in the case of close binaries where rotation and mass transfer may be important. Among compact stars, these may include pulsars and X-ray binaries, where the space velocities reveal important information about natal kicks. Additionally, some X-ray binaries may be detected in quiescence, allowing precise positional information that can be used to identify correct optical/IR counterparts, even in dense star fields.
In summary, such a wide-area survey will image all radio-loud SMBHs in the observable sky down to 1 mJy at mas-scales, allowing unique tests of galaxy formation at the sites of AGN activity, and will provide almost a million radio sources for ancillary and legacy science.","Overall, we envisage minimum resources needed from the LBO to support the all-sky legacy survey.
The proposed legacy survey and commensurate observing programme will require standard VLBA resources from the LBO, given the strategy and recording-rate (4 Gbps). The survey pointings, key files and correlation phase centres for the survey component will be supplied by members of the survey team for execution by the LBO, and standard observing key files will be supplied for the community to use for the commensurate observing programme. The management of the data stream and the correlated visibilities will be supplied by the LBO, although additional off-site correlation may be possible using the current correlator capacity in Bonn (Germany) or at JIVE (the Netherlands), or through the new AVN correlator planned for construction at Hartebeesthoek (South Africa).
The data processing will be carried out using standard calibration scripts within CASA that are currently being developed by team members at ASTRON, JIVE and U. Pretoria. As part of the legacy component of this proposal, the survey team will ensure that VLBI observations can be fully processed within CASA in an automated way, as this package is now widely used for VLA and ALMA data processing, which will help in growing the cm-wavelength VLBI community in the future and at least allow experienced radio astronomers to understand the processes used to calibrate the raw visibilities from the survey. Moving VLBI data analysis to CASA, which will be supported long-term, is also important for building and maintaining the VLBI user capacity. The data archiving of the high-frequency and -time resolution visibility data products will be supplied by the survey team using internal resources. Archiving and data dissemination of lower quality data products (machine readable catalogues, FITS images, low-frequency and -time resolution visibility datasets) will be made available from multiple data centres, including at the LBO.
The expected total data rate post-correlation is ~137 TB for the full survey of ~4 million phase centres with 4 pols and 512 MHz bandwidth; this assumes 34 MB for each phase centre, with 10 VLBA antennas recording at 4 Gbps and 90 s on-source. To help the working group test this survey strategy/set-up (RFI, calibration issues), we will request observations on test fields at L- and C-band (through DDT) before the proposal call.
The survey team and the data processing and archiving resources will be supported through national funding instruments (MPG-Germany, NRF-SA, NSF-US, STFC-UK, NWO-NL), some of which are already in place. Additional funding proposals to support PhD and Postdoctoral Fellows will also be submitted by the individual science teams once an extra-large proposal is approved, so that they are commensurate with the execution of the survey.","The ambitious nature of the all-sky legacy survey needed to achieve our science goals lends itself to an extra-large proposal. For example, the pilot projects for the proposed survey have been carried out using large proposals to the VLBA (~400 h). In order to make the required leap forward, we must increase the overall area by 2 orders of magnitude. This can only be done with surveys that have 2000 to 5000 h on-source, and therefore require the significant amount of time available from an extra-large proposal call.
As part of the comparative studies that our working group is carrying out to define the overall survey strategy, we will determine the optimum observing time needed to maximise the scientific goals of a legacy survey, while not being to the detriment of regular PI-led proposals to the VLBA. Even though many such projects would benefit from the large parent sample provided by a wide-area survey, these regular PI-led proposals are particularly important for developing the VLBI community at PhD and Postdoc level. Nevertheless, given the depth and survey area needed, a wide-area survey will exceed what is available under the standard large proposal call."
A broadband 1-2 GHz polarization survey in the northern sky,mao@mpifr-bonn.mpg.de,Sui Ann Mao (MPIfR),"Bryan Gaensler (Dunlap Institute), Larry Rudnick (U Minnesota), Rainer Beck (MPIfR), Claire Chandler (NRAO), Frank Schinzel (NRAO), Shane O’Sullivan (Hamburg), Aritra Basu (U Bielefeld), George Heald (CSIRO)",2500,0,0,"
This project aims to greatly enhance the polarization and total intensity product of the on-going VLA Sky Survey by conducting follow-up snapshot L band (1-2GHz) observations of polarized sources detected in the VLASS at DEC>+30 deg. Performing on-axis snapshot observations of all polarized sources detected in the VLASS at DEC>+30 deg (~6e4 sources) requires ~ 2 min per source, totaling ~ 2000 hours on-source time. Assuming ~25% overhead for calibration, we require ~ 2500 hours of observing time. This dataset will have legacy value even beyond the Square Kilometre Array era.","The main motivation behind this L band survey is to greatly enhance the VLASS S-band polarization data by providing a much larger lever-arm in wavelength^2 space for Faraday depth determination and depolarization studies. One of the main reasons that VLASS is selected to cover the 2-4 GHz range is because the WODAN survey was covering the 20cm band. The original plan was to use joint WODAN-VLASS data to study broadband polarization properties of extragalactic sources. Now that WODAN is being descoped - it will no longer be a full northern sky survey (APERTIF medium-shallow survey will only cover ~ 3500 deg^2), plus it is not broadband (~300 MHz), and is ~5 times worse in angular resolution (15”) compared to the VLASS (2.5” middle of S band). To have a matched angular resolution L band data to achieve higher precision Faraday depths for the part of the sky not visible from southern sky instruments (POSSUM, MEERKAT and the eventual Square Kilometre Array), we need to employ the Very Large Array itself. The proposed L band observations and VLASS S band data together will enable us to do even better on the original VLASS polarization science goals: we will better characterize properties of the magneto-ionic medium in AGNs and in galaxies across a wide range of redshifts from the much improved Faraday depth resolution and wavelength-depolarization information. (For details of the specific VLASS science goals, see Lacy et al. in prep and Mao et al. 2014)

The much broader wavelength^2 coverage with the joint L+S band data will improve the resolution in Faraday depth space from ~ 200 rad/m^2 (S band only) to 40 rad /m^2 (L+S band). This corresponds to 5 times more precise Faraday depth at the same S/N level. Rotation measure grid experiments used to probe magnetic fields in the foreground medium, especially those expected from objects with weak coherent magnetic fields, or low electron densities that would produce small Faraday depths would especially benefit from this significant decrease in the associated Faraday depth uncertainties. In addition, for sources which have Faraday structures on scales < 200 rad/m^2 (and appear to be Faraday simple - point source in Faraday depth space using S band data alone), the addition of new L band observations means that Faraday depth components within the broad S band PSF can now be resolved in Faraday depth space, allowing us to better characterize the broadband polarization properties of these sources and extract more physics out of the now even broader band data. Wavelength-dependent depolarization of extragalactic sources can certainly be better studied with the proposed L band observations, supplementing the VLASS polarization data at S band.

In addition to polarization studies, the proposed L band survey will be invaluable for Stokes I total intensity studies as well. The proposed L band observations in combination with VLASS would get us another octave of coverage for broadband SEDs, therefore, more precise spectral indices and better measurements of spectral curvature. Many AGNs start to show a spectral turnover at 1 GHz, and the L band observations will be a spectacular survey of them, thereby probing AGN environments and AGN evolution. There will be additional added value by combining these data with the LoTSS survey (Shimwell et al. 2017) with LOFAR, providing ultra-broadband spectra to fully characterize these turnovers (see for example. Callingham et al. 2015, ApJ, 809, 168; Callingham et al. 2017, 839, 174).

From a practical point of view: at DEC >+30 deg, with an estimated polarized source count of 6 sources/deg^2, we expect to have a total of ~ 6e4 sources with S/N>10 in polarization in the VLASS (Lacy et al. in prep, Mao et al. 2014). Assuming flat spectral index, to reach 69 uJy/beam also at L band A array using robust weighting requires ~1m44s per source. So it takes ~ 2000 hours on-source to observe all VLASS polarized sources at L band at DEC>+30 deg. We note that the proposed on-axis observations are highly advantageous for polarization calibration purposes - they will be free of off-axis instrumental polarization effects.",-,The proposed observing time of ~ 2500 hours is well beyond the scale of a regular Large Proposal.
The VLA deep (quasar) fields,ebanados@carnegiescience.edu,Eduardo Banados,"Chris Carilli,
Roberto Decarli,
Dominik Riechers,
Chiara Mazzucchelli,
Masafusa Onoue
Bram Venemans,
Fabian Walter",1430,0,0,"We propose to carry out deep (~2 uJy rms), multi-frequency (L, S, C, Q/Ka-bands) VLA observations of ten fields spread all over the sky. The fields will be selected to be around the highest redshift quasars with the best ancillary datasets (e.g., HST, Chandra, MUSE, ALMA, Spitzer) and spanning a range of key properties. This program will enable unprecedented studies of the highest-redshift quasars and their environments as well as provide a rich legacy dataset for detailed studies of galaxy evolution in different regions of the sky, minimizing the impact of cosmic variance.

The multi-frequency VLA data will be fundamental for the characterization of the radio sources, while the ancillary data will be critical to put the VLA data in context and have the ability to provide photometric redshifts of the radio sources. This program will complement ongoing and future VLA wide and deep survey efforts and will facilitate a plethora of community studies. For example, this proposal has the potential to reveal fainter radio AGN at the same redshift of the targeted quasars and to provide a census of the obscured AGN across all cosmic history.","We propose to carry out an unprecedented, ambitious, multi-frequency VLA deep field. Unlike typical deep fields covering a contiguous region of the sky, here we propose 10 different pointings spread all over the sky. This strategy will provide a less biased view of the universe, minimizing the impact of cosmic variance. This program will therefore complement shallow/wide VLA surveys (e.g., VLASS; Lacy et al. in prep.) and deep/pointed VLA efforts (e.g., VLA-COSMOS 3GHz, Smolcic et al. 2017; Lockman Hole, Condon et al. 2012), while at the same time enabling ambitious science cases that would be impossible to carry out with other deep fields and/or regular PI-led programs.

A key characteristic of traditional deep surveys is to count with a wealth of multi-wavelength information to put the data in context and explore the underlying physics of the astronomical sources. As a matter of fact, it turns out that a large fraction of the highest redshift (z~>6) quasars already have deep follow-up datasets taken with some of the most powerful telescopes on Earth and space (8-10m class telescopes, ALMA, HST, Chandra, Spitzer, etc). As a consequence, regions around the highest redshift quasars are ideal areas for the VLA deep fields. This strategy will allow us to address outstanding questions about the early universe that would be otherwise nearly impossible to tackle via regular PI-led proposals (due to the prohibitive time required as discussed below). These observations will naturally produce a huge legacy for the study of not only high-redshift quasars and their surroundings but a myriad of studies across the entire universe (see below).

The VLA deep (quasar) fields:

We will select fields with the best existing ancillary data and propose for additional observations for some fields if required. We will also prioritize targets that will be observed by LSST and Euclid, which are expected to start taking data in the early 2020s.

We will carefully select quasars covering a range of properties to test potential different environments at the highest redshifts. For example, quasars with weak and normal emission lines (e.g., Banados et al. 2016), radio-loud and radio-quiet quasars (Banados et al. 2015, 2018b), with a range of black hole masses (e.g., Mazzucchelli et al. 2017b), showing signs of extreme outflows (e.g., Banados et al 2018a), and/or quasars with companion dusty galaxies (e.g., Decarli et al. 2017).

The proposed dataset will enable us to address key outstanding puzzles of the highest redshift quasars:

- Theoretical models predict that the highest redshift quasars should be highly biased tracers of the underlying dark matter distribution, signposting the first overdensities of galaxies, or protoclusters (Costa et al. 2014). Thus far, rest-frame UV/optical studies have been inconclusive (e.g., Banados et al. 2013, Mazzucchelli et al. 2017a, Ota et al. 2018). However, recent ALMA observations revealed a population of dusty companion galaxies at small separations from the quasars (Decarli et al. 2017). The proposed deep VLA observations have the potential to reveal faint radio AGN or dusty star-forming galaxies associated with these quasars. Recent studies of radio-AGN show that they are highly clustered (Hale et al. 2018), which increase the chances of finding overdensities of radio sources around the highest redshift quasars (especially the radio loud ones).

- If the radio sources have counterparts in the ancillary data with a photometric redshift consistent (or higher) than that of the central quasars, this would make them automatically prime targets for follow-up studies with JWST.

- Understanding the co-evolution of supermassive black holes and galaxies at the highest redshifts is a key topic in modern astrophysics. A detailed study of the molecular gas of these quasars is fundamental as is both the fuel for star-formation and black hole growth. The large amounts of dust and gas observed in these quasars suggests that they live in some of the most massive earliest galaxies (e.g., Venemans et al. 2017) but to obtain a total molecular mass, constraints on low-excitation CO transitions are required (e.g., Carilli & Walter 2013). Those observations are particularly expensive at high redshift. Indeed, to date CO(2-1) measurements within the first billion years of the universe have been reported only once and only in one of the most extreme (and luminous) quasars known (Stefan et al. 2015). These proposed observations will increase the number of CO(2-1) measurements at the highest redshifts by an order of magnitude.

Sources and requirements:

We aim at detecting 10uJy continuum sources with a S/N>5 in the L, S, and C-bands at matched resolution. This is similar to other deep surveys (c.f., Smolcic et al. 2017) and is enough to detect faint radio galaxies to the highest redshifts. The multi-frequency VLA data will be fundamental for the characterization of the radio sources.

To reach an rms of ~2uJy per beam at 2-3” resolution per field we need:

- L-band (1.4 GHz, A-config): 30 hours
- S-band (3.0 GHz, AB-config): 10 hours
- C-band (6.0 GHz, B-config): 3 hours

To robustly (>10-sigma) detect the low excitation CO(2-1) emission for the highest redshift quasars in the Q/Ka bands (depending on the exact redshift) we require around 100 hours per object.

We note that typical HST multi-wavelength coverage of these fields is about 25 arcmin2, the VLA does not require mosaicking to cover such a region even in the C-band. Therefore, we will require 10x(30+10+3+100) ~ 1430 hours to complete this VLA X-proposal.

The deep fields legacy science:

Besides the fact that these fields contain a high-redshift quasar by construction, they are otherwise perfect “blank fields” at any other redshift and therefore suitable for unbiased studies of galaxy evolution across cosmic time. This X-proposal will enable a countless number of projects, for instance:

- The search for faint high-redshift radio galaxy candidates (e.g., Saxena et al. 2018)

- In combination with the deep X-ray data in some of these fields (e.g., Nanni et al. 2018), the proposed data can provide a census of the obscured AGN across all cosmic history.

- The Q/Ka-band observations to measure the CO(2-1) transition in the highest-redshift quasars will also cover CO(1-0) in a broad redshift range around z~3, near the peak of both AGN and star-formation activity.

- Using the photometric redshift information, the VLA data will enable to study the evolution of the clustering of faint radio sources.

In summary, with this X-proposal will be address key outstanding questions about the earliest universe, while providing a rich dataset to the entire astronomical community.

References:

Banados et al. 2013, ApJ 773, 178 - Banados et al. 2015, ApJ 804, 118 - Banados et al. 2016, ApJS 227, 11 - Banados et al. 2018a, Nature 553, 473 - Banados et al. 2018b, ApJ, 861, L14 - Carilli & Walter 2013 ARA&A 51, 105 - Condon et al. 2012 ApJ, 758, 23 - Costa et al. 2014, MNRAS 439, 2146 - Decarli et al. 2017, Nature 545, 457 - Hale et al. 2018, MNRAS 474, 4133 - Mazzucchelli et al. 2017a ApJ 834, 83 - Mazzucchelli et al. 2017b ApJ 849, 91- Nanni et al. 2018, A&A 614, A121- Smolcic et al. 2017 A&A 602, A1 - Saxena et al. 2018, MNRAS 475, 5041 - Stefan et al. 2015, MNRAS 451, 1713 - Ota et al. 2018, ApJ 856, 109 - Venemans et al. 2017, ApJ 837, 146","Computation facilities to process the data and host the deliverables.
Support with data reduction.",
"The Evolution of the Intra-cluster Medium in the First Super-Sample of SZ, Lensi",sdicker@hep.upenn.edu,Simon Dicker,"Mark Brodwin
Mark Devlin
Brian Mason
Tony Mroczkowski
Charles Romero
Craig Sarzain
Jon Sievers",0,1500,0,"One of the prime motivations for building MUSTANG/MUSTANG 2 was to make high resolution observations of the Sunyaev-Zel'dovich Effect (SZ) in clusters of galaxies. Since MUSTANG2 became operational, many hundreds of hours of high frequency observing time has been awarded to proposals to study single clusters or small (5 to 10) samples of clusters. Although these observations have produced interesting results they do not represent a systematic study of clusters and their evolution across a wide range of redshifts and masses nor are the samples large enough to bring out systematic effects such as selection bias. Instead of drawing a cluster sample from a single catalog such as SZ selected clusters (eg ACTpol), or optically selected clusters (eg HSC), this proposal would aim to survey a wider range of clusters selected to cover moderate to high redshifts and different mass ranges. With such a sample it would be possible to look for the evolution of pressure profiles, the frequency of mergers, how much variation there is in non-thermal pressure support and much more. Publically available data products would be released periodically throughout the lifetime of the project.","Introduction:

Galaxy clusters are powerful cosmological probes. Their spatial density as a function of mass and redshift are related to the underlying cosmological parameters and thus galaxy cluster surveys can be used to constrain these cosmological parameters. Deep observations with high spatial resolution can not only estimate the mass of galaxy clusters, but also illuminate the thermodynamic properties of the intracluster medium (ICM). Understanding cluster physics and its evolution with time is of equal interest to the use of galaxy clusters as cosmic probes. One technique for observing the ICM is to use the Sunyaev-Zel’dovich (SZ) effect - the inverse Compton scattering of CMB photons off hot electrons. The resulting distortion in the spectrum of the CMB is proportional to the electron pressure integrated along the line of sight. The total integrated SZ signal across the whole cluster, Y, is a good proxy for cluster mass and is highly complementary to other techniques as it does not suffer from cosmological dimming.

Current surveys, notably in the X-ray, optical, infrared, and Sunyaev-Zel’dovich (SZ), are extending towards galaxy clusters of lower mass and higher redshift. While MUSTANG-2 is not a survey instrument, it excels as a follow up instrument in this moderate-to-high redshift regime thanks to its sensitivity, high resolution (9 arcseconds) and field-of-view (4.2 arcminutes). This is reflected in the amount of high frequency time, many 100’s of hours, that has been awarded by the GBT TAC for proposals to observe single clusters or to follow up small (5 to 10) subsets of larger surveys. However, in order to reach its full potential a single large sample covering a wide range of clusters at moderate to high redshifts would be far more valuable than a collection of smaller samples with different criteria, depths and data reductions. Such a sample would allow a systematic study of how clusters change with redshift. By drawing the sample from many different surveys, selection biases would become apparent. The frequency of mergers as a function of redshift and the effects of mergers on the mass-scaling relationships used by cluster surveys to obtain masses would be better understood.

Pressure Profiles:

With the resolution provided by MUSTANG-2, the thermal pressure constraints can take the form of pressure profiles, which are found to be surprisingly self-similar (see, e.g. Kratsov & Borgani 2012 for a review). This also manifests itself in the integrated SZ signal ,in its various forms: “integrated Y”, being a desirable observable to scale to mass, to thus improve cosmological constraints. Pressure is also a fundamental thermodynamic quantity which provides insight into ICM physics and the environment for galaxies within the galaxy clusters.

One aim of this project is to place tight constraints on integrated Y for a statistically significant sample across a range of redshifts, masses, and crucially drawn from different (wavelength) catalogs. In order to place tight constraints on the integrated Y, we require more than just a detection of a cluster. While a sample is yet to be selected, the typical cluster would require sensitive measurements out to a radius of 1’. Because processing MUSTANG-2 data will still filter some SZ signal, our integrated Y measurement will be calculated from a non-parametric pressure profile fit. This is a critical point: our integrated Y does not rely on a model (parametric profile) determined from other clusters.

Scaling relations/Biases:

While the low scatter in the Y-M relation makes SZ observations of clusters desirable, with the impending (new) IR (e.g. WFIRST), X-ray (e.g. eRosita), and optical (e.g. HSC, and later LSST) surveys, it will be of further importance to advance their respective scaling relations and understand their selection functions. IR and optical surveys generally rely on an optical richness-to-mass relation (e.g. Rozo et al. 2009), although surveys like that of HSC are utilizing the power of weak lensing / shear to directly estimate the mass. X-ray surveys make use of Tx or LX as mass proxies. While potentially significant variations in core X-ray luminosities have been known for a while, Mantz et. al. (2018) have recently shown the core-excised luminosity to be an efficient mass proxy for use in upcoming surveys.

A more pressing concern with the scaling relations is the offset between N200 (galaxy count within R200, i.e. richness) vs Y500 as shown in Allen et al. (2011). The origin of this offset is not yet understood, but is perhaps not too surprising as the two measurements trace fundamentally different physical regimes (ICM vs. stellar light from within the galaxies). To further emphasize this, the X-ray and SZ scaling relations (both tracing the ICM) are in good agreement (as illustrated in Allen et al. 2011).

This offset, and the fact that different physical entities/processes are being probed at these different wavelengths also ushers in the question of selection bias. Each is clearly prone to their own form of Malmquist bias, selecting those systems which appear significantly to them. X-rays observations are biased towards detecting denser gas (emissivity ~ n2), and thus towards cool core clusters, while IR / optical surveys will be biased towards systems which enhance starlight, thus likely some favoring of star formation. Of course, one may also look at broader biases / covariances, as in Andreon et. al. (2018), which show that fgas has a dependence on cluster mass, where fgas is larger for larger halo masses, which would reduce the yield from X-ray and SZ surveys at the low-mass end. Even if fgas does not have a trend, the scatter alone is indicative that X-ray and SZ surveys are biased to finding clusters with higher fgas.

As studies like Ge et al. (2018) work towards resolving X-ray - richness discrepancies at the high-mass, low redshift (0.1 < z < 0.3) regime, it is not clear that resolutions brought about in this regime will transfer to the low-mass, high-redshift regime. While the agreement between X-ray and SZ scaling relations might incentivize a focus on resolving the SZ-richness discrepancy, it is equally important to reassure general agreement between the SZ and X-ray scaling relations in this regime. Finally, it is also important to check for potential systematics in SZ surveys which do not have the same resolution and potential sensitivity as MUSTANG-2. At the low-mass, high redshift end, the lack of resolution makes SZ surveys susceptible to point source contamination, thus yielding lower mass estimates.

Augmentation with other data sets:

In combination with X-ray maps, lensing maps, or galaxy distributions, potentially much more can be constrained. Owing to low photon counts for the low mass, high redshift clusters, X-ray data will have minimal temperature constraints. However, it should still provide electron density profiles, which in tandem with SZ pressure profiles can yield temperature profiles and subsequently entropy (proxy) profiles. We then have access to the most widely studied thermodynamic quantities within the ICM.

For clusters without X-ray data, that is, selected by richness, potentially with or without weak lensing constraints, we can note any offset between the centroids of the ICM and galaxies. With lensing data, we can also note offsets of the ICM and total (primarily dark matter) mass. Even with electron density constraints from X-rays, one can also place loose constraints on f_gas.

In all cases, targeting for high signal-to-noise observations (for an expected ICM) also means that any null detection should (1) occur rarely in our sample, and (2) be an interesting result in itself.

Conclusions:

In order to have a significant number of clusters in each redshift/mass range we would need to map over 150 clusters and to be sure of detection this would require an average of 10 hours of telescope time each. The exact survey design (target depths, mass ranges and so on) will be worked out in more detail with as much input from the community as possible. Part of that planning would be for the release of finished data products in forms that are most useful for others. At a minimum, this includes reduced maps and associated transfer functions. Ostensibly associated pressure profiles, and ancillary data (e.g. fitted point source flux densities) would be included in a timely fashion as well. The data set from this X proposal would serve not only to produce immediate science, such as comparing scaling relations across wavelengths, but also to produce a public legacy archive which serves to deepen the community’s knowledge of galaxy clusters.","Observations would be carried out using MUSTANG2 on the GBT. By far the largest effort would be manpower, both to carry out observations and reduce the data. This would fall on the MUSTANG2 team not the observatory.

The planned live photogrammetry system for the GBT will likely reduce overheads, improve beam fidelity, and allow for high-frequency daytime observations.","The central tenet of this project is to statistically characterize the ICM of clusters selected by diverse means. That is, for each source survey, we require a statistically relevant sample size. Given that we wish to pull from at least three survey regimes (IR/optical, X-ray, and SZ), 150 clusters offers a truly robust statistical sampling across these regimes - a sample size requiring far more hours of telescope time than a typical large proposal. The desire is to create unifying criteria across these surveys, while still recognizing that many of these surveys are ongoing or have not started yet. Thus, there will be a requirement to select our sample as the project/surveys progress."
Radio Stars in the Gaia Era: Stellar Activity and Planetary Habitability,osten@stsci.edu,Rachel Osten,"[alphabetical list] Geoffrey Bower (ASIAA), Adam Burgasser (UCSD), Jan Forbrich (U. Hertfordshire), Gregg Hallinan (Caltech), Melodie Kao (Arizona State U.), Laurent Loinard (UNAM), Carl Melis (UCSD), Jackie Villadsen (NRAO), Peter Williams (CfA)",1200,0,0,"If NRAO approves the eXtra-large proposal category, we would be interested in submitting a proposal to study stars as radio Suns. Specifically, we would propose to observe the nearby stars within a volume of 10 pc accessible to the JVLA, providing deep and multi-frequency observations to characterize the radio flux density as a function of time, frequency, and polarization. The goal would be to cover a good fraction of each star’s rotation period, and orbital periods for known short-period companions. This would enable answers to questions about the stars themselves, such as the role of strong magnetic fields in producing particle acceleration or potentially thermal emission, as well as probing the near stellar environment. In the era of exoplanets, these measurements enable critical constraints on how the stars affect their near environment, necessary for a more complete assessment of star-planet interaction.","The original VLA had a major impact on all areas of stellar astrophysics; its significant increase in sensitivity and precise localization were instrumental in cementing radio emission as a tool to investigate topics in stellar astrophysics, from mass loss to accretion to magnetic processes. The JVLA’s leap in sensitivity is already returning dividends for making further advances on these topics. There is a revolution afoot in stellar astrophysics, guided by the stunning current and future results from the Gaia observatory, and the wealth of information being returned on nearby stars within the context of extrasolar planet searches. We will have constraints on fundamental properties of a large fraction of the stars in the galaxy within the next few years: three dimensional positions, velocities, ages, and rotation periods, completing the quest for this knowledge that started with the Greeks thousands of years ago.

While large surveys such as the VLASS have a stellar science component within its grasp, the thorough exploitation of the time domain in stellar astronomy is not within its purview. Much knowledge has been gleaned about the role of magnetic fields and accelerated particles, and the impact of mass loss and atmospheric structure, from deep, multi-epoch and multi-frequency observations. These approaches are typically done utilizing one or a few targets per proposal, seeking deep exposures; the very opposite of what a broad and wide survey can accomplish. Yet the single pointings return much more information about flux density variability, spectral energy distribution changes, and polarization changes, than possible with a wide survey approach. A particularly interesting recent development has been the detection of substellar objects which appear to exhibit a wide variety of light curves, from nearly steady fluxes to flare dominated emission, and from rotation-modulated light curves to regularly pulsed emission.

Here, we propose an audacious step forward that promises to change fundamentally the field of stellar and sub-stellar radio astronomy. The approach is a deep, volume-limited survey of all stellar and sub-stellar systems accessible to the JVLA within 10 pc, to probe the time and frequency domain. The RECONS survey (http://www.recons.org/census.posted.htm) is an up-to-date census of all systems within 10 pc of the Sun that will serve as our input catalog. It contains a total of 317 systems that correspond to 232 single stars, 66 binary systems and 19 triple or higher order systems. Together these systems contain 462 distinct individual objects corresponding to roughly 350 G, K, and M dwarfs, a handful of F and A stars, 50 brown dwarfs, and 34 currently known planets (not counting the Solar system planets). Roughly 75% of these systems (240 systems containing 350 individual objects) are located at declinations higher than -30 degrees and are, therefore, visible from the VLA. A systematic survey of this sample will enable us to examine the prevalence of radio emission along the lower main sequence as a function of spectral type, multiplicity, and rotation period. It will also enable us to assess the effect of the presence of planets on the radio emission of the host star, with direct implications for exo-space weather.

Previous surveys of the local solar neighborhood have concentrated on shallow single frequency pointings, or deeper exposures of a limited number of targets. The difference with the current approach is to achieve both deep exposures and ones that cover the microwave band, enabling time, frequency, and polarization coverage (circular polarization is the dominant type for cool stars) for a large number of stars and substellar objects. By covering all of the targets within the 10 pc local volume, this will be the definitive source for understanding large scale magnetic fields and particle acceleration in stellar sources. These types of information are necessary ingredients going forward in understanding the diversity of stellar radio phenomena, as well as placing that understanding within the context of its impact on planetary systems.

Our goal will be to cover the frequency range from 2 to 12 GHz (S, C, and X bands) using subarrays for a subset of objects in order to meaningfully explore the frequency and time domains. The survey will mostly be carried out using C configuration, since we do not expect the emission from individual stars to be resolved even at the highest angular resolution of the VLA. (We avoid D configuration to remove the issue of hitting the confusion limit for the angular resolution at the smallest frequencies). For the multiple systems in the sample, however, we will use the most extended, A and B, configurations. This would correspond to less than 20% of the total observing time. We aim to sample at least a significant fraction of a full stellar rotation period for single stars, and a significant fraction of an orbital period for multiple systems, to accomplish a sampling that is unbiased in time. This translates to an average of about 5 hours per system, and a total 1,200 hours for the sample of 240 systems considered here.

The centimeter wavelength region is particularly ripe for discovery due to the overlap of several potential emission mechanisms (coherent plasma and/or cyclotron emissions, incoherent nonthermal gyrosynchrotron emission, potentially even thermal emission from chromospheres and winds). Many of these mechanisms may exist on the same star, discernable at different times due to changes of magnetic field and density with both time and position on the stellar disk from rotation of starspots/active regions. Snapshot observations would not capture this diversity of behavior.","Carrying out the observations proposed here will require some scheduling flexibility and an intensive use of sub-arrays. Specifically, we would need 3-bit subarrays for C and X band (currently 3-bit sampling with subarrays is a RSRO capability).

Although we do expect to have sufficient resources available to the team, some level of access to NRAO computing resources would be essential or at least helpful.","The expected approximate total time request is 1200 hours, which puts it above the limit of what is feasible to proposal as a large proposal, and into the eXtra-Large Proposal category.

Recent discoveries in stellar radio astronomy have tended to be more serendipitous in nature, rather than following a discrete hypothesis-driven formality. For instance, the discovery of radio emission in ultracool stellar objects in 2001 (Berger et al. 2001) was completely unanticipated based on expectations for behavior from higher mass stellar objects. Likewise, the suggestion of a new emission mechanism dominating some types of low mass stars (Hallinan et al. 2006) was not predictable based on prior understanding, and the very recent discovery of strong magnetism in a planetary mass object (Kao et al. 2018) would not have been expected extrapolating from behavior of giant planets in the solar system. The recent discovery of unanticipated mm flares on Proxima Centauri by MacGregor et al. (2018) similarly demonstrates the discovery potential for magnetic activity in the radio domain. While it is true that one approach to achieving the science proposed here could be multitudes of smaller proposals submitted at each proposal deadline, this would lead to a very biased interpretation of the results. Even submitted as a large proposal, the time constraint of a few to several hundred hours would only enable shallower constraints on each star, or a much shallower volume limit. There is less incentive to undertake this process one star at a time, but it is much more imperative to understand the class of objects. All of these nearby stars are targets for near-term and longer term planet searches, such that by the middle of the 2020s we are likely to know which of these stars host planets and what the characteristics of those planetary systems are.

The astute reader may ask what the overlap is between the science discussed in this EOI and a similar science case contained within the Very Large Array Sky Survey, which does discuss coronal magnetic activity (Lacy et al. 2018). VLASS is designed to provide all sky coverage, and therefore the sensitivity per epoch and duration of each epoch is extremely shallow; only a few seconds on source using on the fly mosaicing, and flux density sensitivity of 120 microJy per epoch (with three epochs planned) at a single frequency band (S band). With a nominal 5 hour per source integration time used in subarrays, this proposed project would achieve rms values closer to about 5 microJy at C, X, and S bands. This provides factors of several to factors of a few tens increase in raw sensitivity; coupled with the wideband frequency coverage and deep time coverage, the discovery potential increases dramatically beyond what can be achieved with the VLASS. We argue that given the increased interest in understanding the environments of potentially habitable planets, a survey like this will have broad interest."
A Legacy Survey of the Local Group and Local Volume,leroy.42@osu.edu,Adam Leroy (OSU) and Karin Sandstrom (UCSD),"Alberto Bolatto (UMD), Laura Chomiuk (MSU), Erwin de Blok (ASTRON), Laura Lopez (OSU), Erik Rosolowsky (Alberta), Fabian Walter (MPIA)",1875,150,0,"If a VLA X-Large call is issued, we would anticipate forming a collaboration to produce extraordinarily detailed line and continuum maps of all accessible Local Group (and possibly just beyond) galaxies. This will enable detailed investigation of the physics of atomic gas, supernova remnants, and HII regions at the scale of individual ISM clouds. Even at the ~1 Mpc distance to Local Group galaxies this is enormously expensive, ~200 hours. But the legacy value would be immense and the maps would be a major resource until well into the ngVLA or SKA phase II era. There is particular synergy with huge (1000+ orbits) recent Hubble efforts to map individual stars across Local Group galaxies and the planned Sloan Digital Sky Survey V “Local Volume Mapper,” which would obtain optical spectra across all of the areas that we propose to map.","The Local Group (d < 1 Mpc) occupies a crucial place in studies of the interstellar medium, star formation, and feedback. The proximity of these nearest galaxies means that the finite resolution achieved by radio and infrared telescopes translates into small physical scales. This, turn, gives access to much more detailed physics than we can study in distant galaxies.

To be concrete: only in the Local Group is the VLA (or any of the SKA precursors) able to map HI on the scale of an individual bound molecular cloud or HII region. And only in the Local Group does the VLA have any prospect to measure individual opaque CNM clouds. Similarly, only at this distance can we resolve turbulence across a large spatial dynamic range or heavily resolve structures smaller than the disk scale height. The large area of these targets also makes absorption studies more powerful (there are more background sources and brighter background sources). And continuum maps in these nearest targets achieve resolution that makes it possible to resolve individual supernova remnants or HII regions.

There is huge interest right now in how the physics of the multiphase ISM interacts with star formation to drive galaxy evolution, chemical enrichment, and feedback into the circum- and intergalactic medium. Much progress will be made in more distant galaxies with models that treat individual clouds, HII regions, supernova remnants, etc. as sub-resolution ensembles. But there is also huge value in studying the physics of the interstellar medium in the only systems where we can actually resolve it while still achieving an external view. ISM studies of the Local Group have been foundational in the past and they will continue to be so moving forward.

With this in mind, if an extra-large call for proposals were issued, we would anticipate proposing for a large program to map all northern Local Group (plus potentially some other key targets out to ~ 3 Mpc, driven largely by overlap with SDSS V - see below) targets in the L-Band targeting HI and radio continuum. The idea would be to spend enough time to get high quality imaging at a few (~5”, heavy time in B config) resolution. This is about 20 pc at the distance to Andromeda (M31) and M33, two of the key targets. It is small enough to resolve individual cold clouds, bubbles, HII regions, supernova remnants and so on. The continuum science here is also excellent, and we would almost certainly also include a 1” (A config) continuum component with a paired S- or C-band component. This would allow finding and characterizing supernova remnants, HII regions, and carrying out detailed absorption studies, among other key science.

LANDSCAPE - HUGE RESOURCES POINTED AT THIS TOPIC:

A major motivator for this is the Fifth Sloan Digital Sky Survey. One of the major components of SDSS V is the “Local Volume Mapper” (LVM) - a program to tackle many of these same themes by obtaining resolved optical spectroscopy across the whole area of these same targets (including M31 and M33). This will yield resolved spectroscopy of the ionized gas at about the same resolution that we propose here, so that the detailed temperature and density structure of the ionized gas in HII regions, supernova remnants, etc. will be known. From LVM and enormous HST surveys carried out over the last few years (PHAT and its extension to M33) the stellar populations are also known in these targets. At the notice-of-intent level, the key thing to realize is that Hubble has sunk many more than 1000 orbits into the Local Group and SDSS V is building a many-million-dollar project to study the same physics we raise here.

THE VLA DOES THIS OR NO ONE DOES:

The VLA remains the major player in studying the northern Local Group for the foreseeable future. WSRT is shifting to survey mode and lacks the capability to reach a few arcsecond resolution anyways. The SKA precursors and SKA phase I, which are in any case comparable to the VLA for this science, are in the south. M31, M33, the northern Local Group dwarfs and the immediate Local Volume will remain the domain of the VLA for the foreseeable future.

PROGRAM SKETCH:

From the HI side, the simple ability to make a high signal-to-noise column density map at 5” resolution requires ~40-60 hours per pointing - targeting 1sigma sensitivity of 1e20 cm^-2 across a 10-15 km/s line requires about 50 hours in B configuration. More modest allocations of a few hours per pointing in D and about 10-15 hours in C are also needed. This is somewhat longer per point than the conventional wisdom from the previous generation surveys (THINGS, LITTLE THINGS, VLA ANGST), because those surveys did not really do most of their work at the limit of the B configuration resolution, and instead did a large amount of science at the C configuration resolution. Here there is huge value in pushing the physical resolution as far down into the “cloud” regime as possible.

In this sense, this project represents an idea that has been suggested and tried several times as the next step for the VLA using HI - pushing the resolution. But rather than emphasizing A config we would use a large amount of time to make very good B configuration maps. Spending something like 50-20-5 hours per point in B-C-D would allow a fantastic 5” map, a great 8-10” resolution cube suitable for line work at a fraction of a km/s resolution with few Kelvin sensitivity.

The continuum coverage obtained at the same time would be very deep, suitable for detailed spectral index maps. For SNR, HII region, and absorption studies, it’s also clear that one would want to add deep integrations in the A configuration (using the same spectral set up as above to allow absorption studies of HI and OH) and a complementary set of shallower observations at S or C band to allow spectral index studies. The continuum sensitivity requirements are less demanding than the line requirements, but the imaging is more challenging, so these are likely to add roughly 20 hours per field (one full 8 hour track in A to ensure best possible u-v coverage and 12 hours spent building the multi-configuration S- or C-band map).

The target selection would focus on all of the gas-rich northern Local Group targets and likely be expanded to include LVM+Hubble targets within 3.5 Mpc (i.e., out to the M81 group). This is about a dozen targets, with M31 and M33 the flagship sample members (then the Local Group star-forming dwarfs IC 10, IC 1613, NGC 6822, Sextans A and B, WLM, etc.). These targets have been observed frequently, but the integration times above dwarf any previous investment and would improve the resolution and sensitivity of the maps enormously. All told this is something like 25 fields observed for ~75-100 hours a piece to do this project right (in reality, we would certainly use more fields and overlap pointings). This is clearly a rough estimate, and one that would be refined and built based on the existing archival data if the project proceeded to a true proposal.

PAYOFF:

In exchange for this investment, the VLA would have a huge impact on SDSS V (some kind of formal partnership could even be imagined), make a big impact on the fields of supernovae, feedback, star formation, and fundamental ISM science. A non-exhaustive list of thing that these data allow include: 1) cloud-scale measurements of how the dust-to-gas ratio varies, 2) absorption line studies of HI and OH across whole galaxies, related back to detailed knowledge of local physical conditions, 3) clear measurements of the scales and locations where clouds become self-gravitating, 4) measurements of how turbulence is driven and how it decays from cloud to galaxy scales, 5) cloud-by-cloud measurements of the conditions for the transition from atomic to molecular gas, 6) measurements of where and how shells and bubbles are carved by stellar feedback into the interstellar medium, 7) cloud scale kinematics, tracing the flow of gas (and presumably metals and dust) through, into, and out of galaxies, 8) the distribution, morphology, and interaction of supernovae relative to the surrounding interstellar medium.

These are big questions that touch many fields of astrophysics. They have been studied extensively, but in each case the detailed view that we have of the Local Group has and will continue to have a big impact. If the VLA moves towards X-Large proposals, spending ~2,000 hours building a defining Local Group legacy would be a great investment.",None.,"The costs to go deep in HI are enormous. We submitted a scaled down version of this proposal about 6 years ago (when the landscape was much less interesting, before SDSS V and the completion of the HST efforts) and we already had to cut corners to bring it down below 1000 hours. Even with this, the scale was just to big for the TAC. But the counter-experience, pursuing this science galaxy-by-galaxy (which is what we shifted) with different approaches has proven problematic. There are insufficient resources, different proposals zoom in on random parts of each galaxy so that legacy value of the observation is diminished. If the VLA wants to produce a definitive set of data on the Local Group that can be used to do science “after the fact” (meaning allow new experiments to be designed after the observations are taken, the approach that has made SDSS and other big surveys so successful) this kind of X-Large approach is a necessity."
An All-Sky Legacy Sample of Massive Galaxy Clusters at z > 1.3,brodwinm@umkc.edu,Mark Brodwin,"Brian Mason, Craig Sarazin, Simon Dicker, Mark Devlin, Tony Mroczkowski, Sara Stanchfield, Charles Romero, Jonathan Sievers, Anthony Gonzalez, Adam Stanford, Daniel Stern, Dominika Wylezalek, Bandon Decker, Christine O'Donnell, Adam Mantz, Peter Eisenhardt and Alexandra Pope",0,1400,0,"MaDCoWS is a comprehensive program to detect and characterize the most
massive galaxy clusters in the universe at 0.8 < z < 1.8, and is the
only all-sky survey sensitive to galaxy clusters at this epoch. The
cluster sample resulting from the overall program is designed to
enable (1) unbiased calibration of scaling relations for cluster mass
estimation techniques, (2) identification of extreme mass sources that
can be used for cosmological studies, (3) strong lensing studies of
clusters and identification of lensed high-z targets for ALMA and
JWST, and (4) investigations of the evolution of massive galaxies in
the most overdense environments close to their epoch of star formation
and mass assembly. We request an eXtra Large Proposal to obtain
high-resolution SZ maps of the complete sample of 70 high-significance
MaDCoWS clusters at 1.3 < z < 1.8 accessible to the GBT. This program
will quintuple the number of extremely distant clusters with ICM
detections in this crucial redshift regime, providing a legacy all-sky
high-z cluster sample of extraordinary scientific value.","The last decade has been a remarkably productive time for the
discovery of z >~ 1 galaxy clusters. Yet despite their successes in
discovering high-redshift clusters, deep X-ray (e.g. Fassbender et
al. 2011; Mehrtens et al. 2012) and Spitzer surveys (e.g. Eisenhardt
et al. 2008; Papovich et al. 2010; Rettura et a. 2014) are limited to
relatively small areas (< 100 deg^2), and thus do not probe the volume
required to meaningfully sample the high-mass end of the z >~ 1
cluster mass function. The South Pole Telescope (SPT, Bleem et al.
2015) and Atacama Cosmology Telescope (ACT, Hasselfield et al. 2013)
Sunyaev-Zel'dovich effect surveys, though much larger, are still
limited to a few thousand square degrees, whereas the all-sky Planck
SZ survey (Planck Collaboration 2014) is primarily limited to z < 0.8
due to its large beam.

The Massive and Distant Clusters of WISE Survey (MaDCoWS, Gettings et
al. 2012; Stanford et al. 2014; Brodwin et al. 2015; Gonzalez et
al. 2015; Mo et al 2018; Gonzalez et al. 2018; Decker et al. in prep,
Moravec et al. in prep) is an IR-selected galaxy cluster survey based
on data from the Wide-field Infrared Survey Explorer (WISE, Wright et
al. 2010). The combination of WISE infrared and wide-field PanSTARRS
optical imaging allows us to robustly identify galaxy clusters at z >~
1 over ~80% of the extragalactic sky. Given the unprecedented volume
surveyed at high redshift, the MaDCoWS sample is expected to contain a
large number of the most massive clusters at z >~ 1, more numerous and
with higher masses than the high-mass, high-redshift tail of the
leading SZ surveys. Indeed, the MaDCoWS clusters are typically as
rich as SZ-selected clusters at the same redshift (Gonzalez et
al. 2018). Spectroscopic (Stanford et al. 2014) and CARMA SZ (Brodwin
et al. 2015) follow-up observations have established that MaDCoWS is
finding massive clusters at z >~ 1, and that the SZ-detected MaDCoWS
clusters occupy the same region in the mass-redshift plane at z > 1 as
the most successful wide-angle cluster surveys. Gonzalez et
al. (2015) reported that MOO J1142+1527 at z = 1.19, with an
SZ-derived total cluster mass in excess of 10^{15} Msun, is the most
massive cluster discovered by any method at z > 1.15, and the second
most massive at z > 1.

We have subsequently obtained IRAC imaging for the top ~2000 WISE
candidates. These data, combined with X-ray/SZ imaging and optical
spectroscopy for a representative sample of massive clusters at z~1,
have allowed us allowed us to refine our photometric redshifts,
identify a subset of the richest --- and likely most massive ---
systems at 0.8 < z < 1.8, and to calibrate a preliminary mass-richness
relation. The very high-z tail of the MaDCoWS sample contains 70
massive (M_{500} >~ 2 x 10^14 Msun) clusters at 1.3 < z < 1.8. We
propose an eXtra-large program to obtain high-resolution MUSTANG-2 SZ
imaging on this legacy sample of the most massive, distant clusters
visible to the GBT. The resulting sample will quintuple the number of
ICM-detected clusters at z > 1.3, enabling multiple groundbreaking
analyses --- both cosmological and involving galaxy and cluster
formation --- that are limited by existing samples. These
investigations all critically depend on getting precise ICM-based
cluster masses, which MUSTANG-2 can deliver through high-resolution
measurement of their SZ decrements.

Unbiased Calibration of Cluster Scaling Relations

Cosmological constraints based on evolution of the cluster abundance
are currently limited by systematic uncertainties in the calibration
of the mass observable for a given survey (e.g. Vikhlinin et al. 2009,
Benson et al. 2013). Scaling relations between the best established
mass estimators --- X-ray gas mass, SZ decrement, and weak-lensing
shear --- thus serve an important role in quantifying any differential
bias in the masses obtained via the different techniques (e.g. Rozo et
al. 2014, von der Linden 2014). A subtle, but important, consideration
is that for clusters selected via either X-ray emission or SZ
decrement the mass estimate derived from that observable will on
average be biased high due to Eddington bias. While one can attempt to
``de-boost'' the inferred mass based upon the expected Eddington bias,
a more robust method of calibrating scaling relations is to use
samples selected on an observable unrelated to the mass estimators
being compared. MaDCoWS provides the only existing high-redshift
sample of massive clusters not selected via the ICM and as such can be
used to better calibrate the high-mass end of these scaling relations.
This legacy sample will also provide compelling targets for high
resolution Chandra imaging, as well as z ~ 1.5 counterparts to the
low-z CLASH/Frontier Fields for gravitational lensing experiments with
HST, JWST, and ALMA.

Strong Lensing Clusters and the Dawn of Galaxies

This legacy sample of the most distant, massive MaDCoWS clusters will
provide compelling z ~ 1.5 counterparts to the low-z CLASH/Frontier
Fields for gravitational lensing experiments with HST, JWST, and ALMA.
This will enable strong lensing mass reconstructions, extend studies
of the cluster mass-concentration relations to the highest redshifts
and, as the system with the largest lensing cross-sections in
existence at z ~ 1.5, this sample will ultimately feed future ALMA and
JWST programs studying galaxy formation and reionization in the early
Universe.

Primordial Non-Gaussianity

Because the most massive galaxy clusters in the Universe assemble the
bulk of their mass at late times, they have long been used to stress
test paradigm models. Studies continue to debate if the most massive
clusters known at z > 1 are consistent with Gaussian density
fluctuations at the end of inflation (e.g. Harrison & Hotchkiss 2013)
or instead require primordial non-Gaussianity on cluster scales (which
is not ruled out by Planck). Evidence favors the null hypothesis, but
a definitive answer remains elusive due to small number
statistics. For a standard Gaussian LCDM cosmology there should be
only ~10 clusters over the entire extraglactic sky at z > 1.3 with
M_{500} > 4 x 10^{14} Msun (Holz & Perlmutter 2012). In this program
we will measure ICM masses for 70 rich z > 1.3 clusters. We will
identify any ``overly massive'' clusters, should they exist, that may
pose a challenge for LCDM and yield interesting constraints on
primordial non-Gaussianity.

The Cosmological f_{gas} Test

Measurement of the X-ray gas mass fraction, f_{gas}, in the largest
dynamically relaxed galaxy clusters provides powerful, competitive
constraints on dark energy (Ettori et al. 2009, Allen et al. 2013,
Mantz et al. 2014). Although the highest redshift clusters provide
the greatest leverage for this test, the best current constraints
include only two at z > 0.8. Allen et al. (2013) show that a sample
with as few as ~10 very massive, relaxed clusters at z > 1 can improve
the figure of merit for the dark energy equation of state by more than
an order of magnitude. The high-resolution pressure maps provided by
MUSTANG-2 will identify *both* Bullet Cluster-like mergers, which have
been used to constrain the nature of dark matter, and very relaxed
systems that have the potential to revolutionize f_{gas} cosmology.

Description of observations

MaDCoWS is the only survey covering nearly the full extragalactic sky
that is sensitive to z > 1 galaxy clusters, and so is best able to
identify the most massive clusters at these redshifts. Using
Spitzer/IRAC imaging of the top 2000 candidates we have ranked our
sample by IR richness, which allows us to isolate and study the most
massive z >~ 1 clusters. Using low-resolution CARMA SZ observations
for a subset of our clusters, we have measured an approximate
mass-richness relation, finding a strong correlation with a scatter of
only ~25%. The IRAC photometry also allows cluster photometric
redshifts accurate to dz ~ 0.03(1+z). For this eXtra-large program,
we have isolated the 70 most distant clusters in the MaDCoWS sample.
These lie at 1.3 < z < 1.8and have richness-based masses in excess of
M_{500} >~ 2 x 10^{14} Msun.

Modeling a Planck-like (Arnaud et al. 2010) M_{500} = 2.0 x 10^{14}
Msun cluster at z = 1.5, we find an on-source exposure time of 10
hours will yield a > 10 sigma map detection, sufficient to identify
mergers and cool-core clusters and simultaneously constrain the
pressure out to r_{500}. Including 100% overhead, with 70 clusters,
we ask for 1400 hours total.","High frequency weather requirements are more demanding, but upgrades
to a live photogrammetry system will improve focusing, reduce
overheads, and potentially allow for daytime observations.",
High-Frequency Galactic Plane Continuum Polarimetry and Line Survey,lsjouwer@nrao.edu,Lorant Sjouwerman (NRAO),"Betsy Mills
Ylva Pihlstrom
Steve Myers",3850,0,0,"We propose a unique mJy/bm sensitive arcsec resolution 15GHz VLA polarization imaging survey of the Galactic Plane using C configuration. A major science driver addressing the need of several community based research topics is to fill the gap between previous low frequency surveys, mainly detecting synchrotron emission, and the sub-mm and infrared surveys that detect thermal radiation. A 15GHz survey is both feasible and maximally unique from the synchrotron radio view and will facilitate new multi-waveband Galactic research and, e.g., identify targets for ALMA. Pending the final survey parameters, a strawman survey with 1 mJy/bm 12-18 GHz detection limit over a 10 degree band along the 280 degree Galactic plane would consume ~3750 hours using on-the-fly mapping and still allow for, e.g., a simultaneous sub-Jy/beam 12 GHz methanol maser survey.

This survey combines the superior sensitivity and angular resolution of the CORNISH survey, with the sky area covered by the low resolution GPA survey, while observing at a frequency comparable to the AT20G survey and would be complementary to the proposed MeerGAL survey. This survey, given the capabilities of the VLA, is long overdue.","We propose a unique mJy/bm sensitive arcsec resolution 15 GHz VLA polarization imaging survey of the Galactic Plane using C configuration. A major science driver addressing the need of several community based research topics is to fill the gap between previous low frequency surveys, mainly detecting synchrotron emission, and the sub-mm and infrared surveys that detect thermal radiation. A 15 GHz survey is both feasible and maximally unique from the synchrotron radio view and will facilitate new multi-waveband Galactic research and, e.g., identify targets for ALMA. Pending the final survey parameters, a strawman survey with 1 mJy/bm 12-18 GHz detection limit over a 10 degree band along the 280 degree Galactic plane would consume ~3750 hours using on-the-fly mapping and still allow for, e.g., a simultaneous sub-Jy/beam 12 GHz methanol maser survey.

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Project Description

We propose a unique mJy-sensitivity arcsec resolution 12-18 GHz survey of the Galactic plane using OTF mapping. The survey is set up to provide and maximize legacy data in a region that is largely unsurveyed at radio frequencies sensitive to thermal emission. Such a survey would yield the least duplication of previous work and thus make the highest possible impact in astrophysics. As homogeneous, sensitive and high resolution radio imaging of the plane, with adequate sensitivity to spectral lines, cannot be done with any other existing instrument it will serve the entire community for years to come.

Scientific motivation

The vast amount of multi-frequency data on the Galactic plane, disk and bulge has been tremendously valuable in the study of dynamics, structure, evolution, physics, chemistry and content of the Milky Way galaxy, its stellar population and other constituents. Because of its proximity, it is in the Galaxy that we can best study the birth of stars, chemical enrichment of molecular clouds, violent environments around exploded stars, orbits of gas and dust and the physics of supermassive black holes, to name a few topics. In the past, the typical approach to studying these topics was to select an area of interest and observe in different wave bands to disentangle the emission from objects from their environment with the highest sensitivity and angular resolution possible to further our knowledge. Surveys were usually done by small groups aiming for a well defined study. However, with the advent of NASA’s Great Observatories and other large missions, the approach has shifted more and more toward surveying large areas yielding legacy data sets that benefit the entire community for a multitude of science goals.

The VLA has performed large area surveys in the past, with the most widely used -- ignoring the currently incomplete VLASS -- being the NVSS (all-sky, 40” resolution at 1.4 GHz) and FIRST (SDSS region, 1” resolution at 1.4 GHz). These surveys, although they have limited angular resolution and sensitivity, still provide the multi-wavelength community with instantaneously available valuable radio data that is otherwise hard to obtain. Nevertheless, the NVSS with its low resolution was confused in the Galactic plane (also partly true for VLASS), especially in the bulge area, and FIRST entirely avoided the Galactic plane. This omission is somewhat ameliorated by the existence of a number of large VLA surveys more focused on the Galaxy, including VGPS, VLA-L, VLA-C and CORNISH. However, although all these surveys were very successful for their dedicated science purposes, they all used frequencies most sensitive to synchrotron radiation. One of the reasons for this, apart from science motivations, is that the large primary beam at low frequencies makes surveying large areas economical in observing time; the low frequencies are ``cheap'' for the potential science return. Observing at low frequencies is of course now cheaper than ever given the new OTF mapping capability of the VLA in combination with the instantaneous high sensitivity of wide observing bands. Yet these capabilities also mean that for the first time ever, efficient surveys of large areas at higher frequencies are achievable: a value that cannot be ignored.

We propose a legacy survey of the Galactic plane at frequencies where continuum emission is less dominated by synchrotron radiation and more of the thermal emission prevails. This survey will be an essential bridge between the synchrotron dominated (VLA) radio surveys and thermal emission dominated infrared surveys like those of MSX, GLIMPSE, WISE, etc. More than in the lower frequency surveys it will highlight (compact) HII regions (and individual Stromgen spheres), planetary nebulae, stellar winds and ionized jets and gas in the ISM, and star forming regions as well as many other compact sources such as flat spectrum extragalactic cores. The latter can be used as high-frequency calibrators (for the VLA, but also ALMA, ATCA, etc) which are relatively rare for high-frequency observations in this region. However, as the current lack of calibrators attests: this is largely unexplored territory.

Ultimately however, we want this survey to function as a valuable resource in its own right. The choice of the wide extent of the Galactic plane is based on its having the least prior radio coverage while also hosting some of the richest multiwavelength coverage (from X-ray to low-band radio), maximizing its potential legacy value. Covering the selected region in full therefore will thus provide a valuable new resource for studies of thermal radio sources, of use to a large community.

There are many possible science cases to argue for a high-frequency, high-resolution radio survey of the plane. To convey the breadth of science that just this survey would enable, we have selected several example cases which illustrate the power of a thermal radio study for better constraining the full life cycle of stars, from birth to death. However, we want to emphasize that the main goal of this survey will be its legacy value to the community for a diversity of science cases.

1. Hypercompact HII Regions:

The formation of massive stars is a swift process, and as a result there are few known examples of distinct early evolutionary phases. Hypercompact HII regions (HCHII) are believed to represent one of the earliest phases of this process, but only a handful are known (e.g., Kurtz 2005). Without better statistics, it is impossible to constrain the lifetime and properties of this stage. With this survey we will be sensitive to these sources at all Galactic radii.

2. High-mass Protostars:

High mass protostars are even earlier phases of high mass star evolution than HCHII. Even fewer of these sources have been characterized, but understanding their properties is critical for modeling accretion growth of massive stars (e.g., Van der Tak & Menten 2005). This survey will be sensitive to radio emission from these sources. Given the larger scale height of such nearby sources, the larger latitude range of this survey will be an advantage in detecting these sources compared to GLOSTAR (using C band) which will eventually cover the Galactic center.

3. Planetary nebulae:

The current census of planetary nebulae in our Galaxy is still highly incomplete, especially toward the high-extinction regions of the plane/bulge, where the greatest density of these sources should be found (Jacoby & Van de Steene 2005). Where optical detection methods fails, other methods such as infrared color identification are possible with recent surveys such as WISE, but are not unambiguous as YSOs and AGB stars have similar colors. Radio spectral indices of these counterparts provided by this survey will aid in detection and positive identification of these missing sources in the plane/bulge, helping constrain the ubiquity of this phase of stellar evolution.

4. Pulsars:

Due to increased scattering at low frequencies toward the center of our Galaxy, it is believed that many pulsars in this region go undetected (e.g., Lazio & Cordes 2008). Although this survey would not resolve pulsed behavior, it would identify a population of compact, steep spectral-index candidate sources for future study. Observations at high frequency can also shed light on the predominance of unusual high-frequency behavior: a number of pulsars have been suggested to have flat or even increasing spectral indices at these and higher frequencies (Kramer et al. 1997).

5. CH3OH Masers:

The high spatial resolution of this survey will yield an extremely sensitive survey of radiatively-excited 12 GHz CH3OH masers, which probe extremely early stages of massive star formation. There are no blind surveys of this maser transition, and although it is typically weaker than its 6 GHz counterpart, it can also be stronger (Caswell et al. 1995). This makes an unbiased survey for the 12 GHz maser sources valuable not just to probe of variations in the physical conditions which give rise to this maser, but also for potentially detecting new sources.

6. H2CO absorption

H2CO is an abundant tracer of the dense gas. Spatial variations in the absorption strength of this line against strong background continuum sources can probe the structure of the dense ISM, as can follow-up observations of absorption variability against point sources (Moore & Marscher 1995). Together with the 4.8 GHz transition of this line, covered in GLOSTAR, it can also be used to directly measure the ISM density toward these regions.

Survey parameters

Our ultimate goal is to provide a milli-Jansky/beam sensitive arcsecond resolution legacy survey of the entire Galactic plane covered by other legacy surveys in other wavelength regimes. The largest coverage is that of MSX, |b|<5deg, which is also covered by the GBT-GPA at single dish resolution. We aim to cover this area of 2800 square degrees with an interferometer at the highest frequency, sensitivity and angular resolution (at least comparable to the best infrared surveys) as pragmatic. This will yield the highest legacy return for such a survey. In practice, with OTF mapping at the VLA this translates to observations in Ku-band (12-18 GHz) as it is more sensitive than observing in the wideband K- or Q-bands, does not require pointing or the best high-frequency observing conditions, and still provides a reasonable primary beam for survey speed. About 1” angular resolution, for a center frequency of 15 GHz, is obtained in the C (1.2”) and B (0.4”) array configurations. The sensitivity resulting from a compromise between maximum survey speed and minimum data rate is of the order of 1 mJy detection limit (RMS∼0.1 mJy/beam), very acceptable for almost any legacy use.

Proposed observations

We propose to use the new OTF capability to image the Galaxy at Ku band (∼12-18 GHz) in C (and CnB) array configuration using X-proposal time. This would be a homogeneous sensitivity continuum coverage of the region mapped by multiple surveys with instruments in other wavebands (optical, infrared, X-rays, mm/dm radio) and is thus of high importance for multi-frequency studies. Such a large region has not been imaged previously in a radio frequency range that is not primarily sensitive to synchrotron radiation nor at such a high angular resolution. We also aim to identify good new high-frequency calibrators for the VLA/VLBA in this region, largely from the new extragalactic background detections.

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Assuming that the AT20G survey is representative for the extragalactic background at 12-18 GHz, with a source count of over 5800 sources down to 45 mJy/beam at Declination <= 0, we can estimate the anticipated number of extragalactic sources by:
5800/20,000 sources per square degree times 2800 square degrees = 812 sources.
Extrapolating to a conservative 10-sigma detection rate of 1 mJy/beam using S^-1.15 (Waldram et al, 2010MNRAS.404.1005W) we will detect 64,000 extragalactic sources in this Galactic plane survey (23/deg2), plus an unknown contribution of Galactic sources which is possibly comparable in the same order of magnitude.

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Survey Strawman Parameters:

Fixed Parameters

Band: Ku 12-18GHz
Field-of-View (primary beam): 2.33' FWHM at 18GHz, 2.8' FWHM at 15GHz
Effective Mosaic Beam Area: 3.08sq.arcmin. at 18GHz, 4.44sq.arcmin. at 15GHz
Array Configuration: C (possibly CnB in South)
Resolution: 2.1"" at 15GHz (natural), 1.4"" at 15GHz (robust), 1.2"" at 17.5GHz (robust)
Raw Continuum Sensitivity (from ECT): 5.5GHz at 15GHz = 226uJy/bm in 1s (robust)
Raw Spectral Sensitivity (from ECT): 1.0GHz at 17.5GHz = 553uJy/bm in 1s (robust)

Selectable Parameters

Survey Area: 2800 sq.deg.
Visibility Integration Time: 1 sec
OTF Row Separation: 1.5' (0.54*FWHM at 15GHz, 0.64*FWHM at 18GHz)
OTF scan rate: 36""/s (0.6'/s) ==> smearing 0.26 x FWHM at 18GHz in 1 integration (severe)

Derived Parameters

Max. Survey Speed (ScanRate*RowSep) = 0.9sq.arcmin/s (=sq.deg./hr.)
Effective On-Sky Intergration Time (BeamArea/SS) = 4.9s at 15GHz, 3.4s at 18GHz
Full-band Continuum Sensitivity = 102uJy/bm (1-sigma)
Spectral Sensitivity (1GHz at 17.5GHz) = 300uJy/bm (1-sigma)
On-Sky Time To Complete Survey (Area/SS) = 3111 hrs

Survey Time including 20% calibration and startup overhead = 3750 hours
Total request with added Ku-band fine-tuning and RFI tests = 3850 hours","The strawman project has these resource considerations:

- We will use Ku-band OTFM mode in C-array configuration, perhaps with some fraction (0.2-0.3) in CnB array configuration for better performance at the lower declinations (negotiable).

- The LST range for the observations will be spread roughly evenly over 0-24h, but likely with a low demand for LST 10-15 where the Galactic Plane is below the horizon.

- We plan to reuse existing VLASS code and workflow with small adjustments to replace S band with Ku band properties and parameters. Whereas reusing the verified VLASS code should carry low risk, there are some differences that need to be addressed.
For this we included ~50h for on-the-sky code/workflow verification tests in the total time request. We also need to anticipate a similar amount of test time to deliberate how to solve for the different RFI environment at Ku band.

- We anticipate access to cluster processing and storage like any normal observing project, although there might be times of high-demand during the observing season possibly warranting requesting a shielded part of the cluster (as with VLASS).
Depending on a dump rate of somewhere between 0.3-1s, the total raw data (archive storage) volume is 400-1200 TB, ignoring possible frequency averaging. Due to the large bandwidth and line setup in combination with OTF dump-rate requirements, this is a high data-rate experiment; the exact setup is negotiable.

- As the PI is an NRAO employee, it seems logical that NRAO also provides the data product hosting service. However, this data product hosting and related service maintenance is negotiable with UNM.

- It is prudent to anticipate AOC access and reserved desk space for one or two collaborators and/or PhD students for the duration of the project.

Note that the number of 3850 hours (including testing) assume a strawman design for a 2800 square degree 1 my/beam detection limit continuum survey. The total area or sensitivity are negotiable up or down, depending on TAC logistics and SRP suggestions.","The large number of hours requested (just under 4000) in a single configuration (which at 100% observing efficiency would take about 6.5 months to complete) implies a multi-year proposal, which are not well handled by the current semester-based SRP and TAC system. We would anticipate that like many such X-proposals, when fully proposed there would be many co-Is that will have conflicts within a standard Galactic SRP and TAC, making evaluation difficult within the standard system. Furthermore, this is a (Galactic focused) general sky survey, and as such covers multiple disciplines and is more of a multi-purpose legacy survey with possible applications per science area (AGN, Galactic SFR, SNR, PNe, radio stars, GMCs, X-ray binaries, pulsars, masers, etc). This, again, makes evaluation and balancing within the current system, which is dominated by a large number of more single-cycle single-focus observations, problematic. This proposal would best fit within a X-proposal system that can deal up front with conflict in setting up the SRP/TAC, take into consideration the multi-year nature of the proposal, and evaluate against proposals of similar scale and intent."
The North American Nanohertz Observatory for Gravitational Waves,pdemores@nrao.edu,Paul Demorest,The NANOGrav Collaboration,1000,4000,0,"The North American Nanohertz Observatory for Gravitational Waves
(NANOGrav) has an ongoing experiment using high-precision pulsar timing
for a goal of direct detection of nanohertz-frequency gravitational
waves (GW). Here, we express interest in a expanded GBT+VLA timing
program aimed at detection of GW from discrete supermassive black hole
binary systems, as opposed to the stochastic GW background that has
typically been the focus of previous work. This program would be
complementary to our ongoing program to detect and explore the
stochastic GWB, although both projects will benefit from combined data.
While this is a long-term project, for purposes of this proposal, we
consider a five-year span from 2020 to 2025. The resulting data set
will also be a rich source of ""secondary"" science for studies of neutron
stars, other tests of gravity, pulsar emission processes, and the
interstellar medium. In addition to the scientific objectives, the
project will provide new technical insight into the use of array
telescopes for high-precision timing; this becomes important looking
ahead to future telescopes such as the ngVLA and SKA.","Detection of gravitational waves (GW) has already provided dramatic,
unexpected new insights about the universe; in direct analogy with
multi-wavelength electromagnetic observations, expanding our reach into
larger portions of the GW spectrum will result in further advances.
Long-term, high-precision timing of an array of millisecond pulsars acts
as a GW detector operating in the nanohertz frequency regime,
complementary to higher-frequency GW experiments such as LIGO. The
range of GW frequencies detectable by pulsar timing is determined by the
observational timespan -- observations spanning >~10-year timescales
open new parameter space as the lower GW frequency bound continues to
decrease. Long data spans also provide improved sensitivity at higher
GW frequencies. Our group, the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav) has been running such a pulsar timing
array experiment using primarily the GBT and Arecibo telescopes for over
a decade. We are writing to express interest in an expansion of the
project over a five-year time scale, aimed at detection of individual GW
sources via high-cadence GBT observations, and including increased use
of the VLA at higher frequencies (above 2 GHz) in order to optimize
timing of larger numbers of pulsars.

In the nHz range, the universe should be awash in GW produced by
in-spiraling supermassive black holes (MBHs) resulting from the mergers
of galaxies (e.g., Jaffe & Backer, 2003). Following a merger of two
host galaxies, their central MBHs will sink towards each other due to
dynamical friction, forming a binary pair. This will eventually decay
due to GW emission, coalescing into a single, more massive MBH. These
sources are visible to pulsar timing when their orbital periods are
~years. The sum of all such binaries creates a stochastic GW background
(GWB). The amplitude of the nHz GWB is highly dependent on the details
of the relationship between black hole mass and other galactic
properties (eg, the M-sigma relation) and other astrophysical
considerations; GWB limits or measurements can distinguish between
various models of MBH binary formation and evolution (Sesana et al.,
2008; Sesana, 2013, Arzoumanian et al 2018).

The stochastic background is composed of many individual supermassive
black holes. As NANOGrav's sensitivity continues to improve -- due both
to an increase in the number of pulsars and the continuing increase in
the length of the data set -- the detection of the nHz GWs from nearby
individual supermassive black holes becomes plausible. These individual
supermassive black holes produce continuous periodic GWs (ie, a
monochromatic signal in the GW spectrm). Indeed, as the occurrence of
supermassive black hole binaries is essentially a stochastic process,
there is some probability that a relatively nearby massive galaxy hosts
a sufficiently loud binary that it would be detectable by NANOGrav in
the project described here.

The NANOGrav observing program began in 2005 with 17 pulsars, and has
grown over time to a total of 74 pulsars currently. These observations
have been optimized primarily for detection of the stochastic GWB, for
which total number of pulsars is the most important factor determining
GW sensitivity. The project currently uses ~560 GBT hours per year; we
expect usage to grow by ~25 hours/year as newly discovered pulsars are
added to the experiment. Sensitivity to continuous GW can be improved
by spending more time on the best and brightest pulsars in the set. We
have recently begun such ""high-cadence"" observations on a limited number
of pulsars with both telescopes. An expanded high-cadence program, in
combination with the ongoing GWB project, would significantly improve
our single-source GW sensitivity. We estimate such a project could be
done with ~800 hours per year on the GBT over a five-year timespan.

Our current GBT observations are done at radio frequencies ranging from
0.7 to 2.0 GHz using two separate receivers. For most pulsars, this
frequency range strikes an optimal balance between pulsar flux (which
declines with observing frequency) and systematic effects due to pulse
propagation in the interstellar medium (these are larger at low
frequencies; see Lam et al 2018 for details). However some of the more
distant pulsars benefit from observation at higher frequencies. Over
the past year we have begun a preliminary timing program at the VLA in
order to take advantage of the improved sensitivity at frequencies above
~2.5 GHz, relative to the GBT. The program has a secondary purpose of
technical development and demonstration of high-precision pulsar timing
with an array; this becomes increasingly important looking ahead to
instruments such as the ngVLA and SKA. In the proposed expanded
project, we envision the VLA playing a larger role, for both these
reasons. The VLA portion of the project could potentially utilize ~200
hours/year, pending a more detailed analysis of the full pulsar source
list.

In addition to GW studies, our project has broad impact across a number
of areas. The long-term data set generated by this project plays a
complementary role to shorter, more intensive projects, including
measurement of binary pulsar orbital parameters, tests of gravitation,
measurement of and exploration of intrinsic pulsar noise properties. We
have undertaken a variety of education, training, and outreach efforts:
The NANOGrav collaboration currently includes 30 postdoctoral
researchers and 24 graduate students (full list available at
nanograv.org/people). Undergraduates are actively involved in our
research as well via a number of programs. In addition, we are
committed to making our observational data products accessible to other
researchers, both raw data and final data products. We have data-sharing
agreements in place with other pulsar researchers, and have been
actively exchanging data sets. With each data release paper the entire
timing data set is made available publicly. We have designed a data
archive system and web interface for sharing pulsar timing data sets and
resulting data products such as calibration and time of arrival
measurements. We would continue to utilize our large amount of previous
experience with data curation to maximize the long-term legacy value to
the entire scientific community of the data obtained via the proposed
project.","NANOGrav has a currently-funded proposal, in collaboration with the GBO,
to design and build a new ""ultra-wideband"" feed and receiver system for
the GBT covering ~0.7--4.0 GHz instantaneously. This will significantly
improve timing sensitivity and reduce ISM-based systematics that arise
in the current two receiver observing strategy. While this is an
existing project and therefore not directly linked to the expansion
proposed here, this receiver will be an integral part of the expanded
observing program. Ongoing Observatory support for commissioning,
optimization, and maintenance of the new receiver system is vital for
success of the project.

Development of pulsar observing capability at the VLA is still
incomplete. In particular, increased Observatory software support for
easier observational setup, scheduling, and archival of VLA pulsar
timing data is necessary for the proposed project to succeed.","The NANOGrav project has already been successful at obtaining observing
time over the past decade via a combination of Regular, Large, and
Sponsored observing proposals to the GBT. However, having to re-propose
every 1--3 years introduces an element of uncertainty to an experiment
where the best results will be achieved on >10-year timescales. An
Xtra-large proposal would help guarantee continuity of the program over
longer timescales. Additionally, the project's telescope time
requirements have grown significantly as the number of pulsars monitored
has increased. This increase is necessary to achieve the required GW
sensitivity, but we are beginning to exceed the ~1000-hour/year regime
that has typically been the maximum for Large Proposals, therefore an
Xtra-large propsal may be more appropriate in the future."

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