2013

by: Erik Tollerud (Yale)

Dwarf galaxies are a frontier for new discoveries in both galaxy formation and cosmology. I discuss work centered around connecting LCDM and its predictions to observations of dwarf galaxies at three different scales of "dwarf". I will discuss the Milky Way's satellites and both solutions and lingering troubles with their abundances and scalings. The strangest of these puzzles manifest in the bright dSphs, which seem to be under-dense relative to LCDM expectations. With this in mind, I present results from a large spectroscopic survey of M31's dSph satellites searching for signs of similar puzzles. These reveal consistency between the Milky Way and M31 satellite populations, showing these puzzles are not unique to the Milky Way. Finally, I will describe a search for bright satellites (analogous to the LMC) in the SDSS, and compare their abundances and properties to straightforward LCDM expectations. These reveal an amazing level of consistency between the SDSS and LCDM for bright satellites. Further, interpreting these galaxies in this LCDM context provides some interesting new questions regarding satellite quenching and the red-blue sequence bimodality. Taken together, these results suggest that there is a particular scale in galaxy formation (at Vcirc~50 km/s), where either LCDM begins to break down or galaxy formation becomes overwhelmingly stochastic.

By: Albert Einstein

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By: Edwin Hubble

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by: Steve Ellingson (Virginia Tech)

The LWA1 radio telescope (also known as the first station of the Long Wavelength Array) is a compact array of about 260 dual-polarized dipoles, collocated with the VLA, operating in the 10-88 MHz range (Ellingson et al. 2013, astro-ph/1204.4816). The instrument provides 4 independently-steerable beams using digital true time delay beamforming, providing large instantaneous bandwidth (up to 17 MHz per beam), high intrinsic sensitivity (about 6 kJy zenith system equivalent flux density, or about 5 Jy/beam for 5 sigma in 1 s), and large field of view (about 3-10 degrees, depending on zenith angle and frequency).  LWA1 has been operating as an "open skies" radio observatory since Spring 2012, and is currently conducting observations supporting research on pulsars, astrophysical transients, cosmology, space weather, the Sun, Jupiter, and the ionosphere.  In this talk  I will review the design and capabilities of the instrument, summarize commissioning results, and present an overview of first science results.  I will conclude with a summary of findings from our ongoing project to monitor the giant pulses of the Crab Nebula pulsar and a concurrent project to search for transients in the form of single dispersed pulses from other sources.

by: Laurent Pagani (Observatory of Paris)

From the moment gas and dust concentrate enough to self-shield against UV, molecules form, temperature drops and cores collapse to form protostars, proto-planetary disks and (at least once) inhabited planets. To understand this evolution, we try to study the different phases with radiotelescopes and IR satellites mostly. We try to understand how long the clouds live, how the prestellar cores form, and finally whether the water on Earth came from comets or not. Deuterium, though playing no major role in all this, appears to be very helpful to understand several aspects of this story. I will illustrate its use with three different examples : cloud age, prestellar core formation speed and core depletion profile studies, all based on DCO+ and/or N2D+ observations and modelling, species for which the GBT now stands on the forefront of the observation tools.

by Alberto D. Bolatto  (University of Maryland)

Daniel Davis & Gary Brown (Virginia Polytechnic Institute & State University)

During the last four years, the ElectroMagnetic Interactions Laboratory has been involved in the modeling, measurement, and analysis of near earth propagation in the 900 to 2,300 MHz frequency band. The modeling phase comprised the application of methods developed to predict the electromagnetic scattering from rough surfaces for radar clutter and remote sensing studies. Some of the difficulties encountered during this part of the research entailed (1) terrain elevation data base incompatibility with the electromagnetic scattering modeling needs, (2) applying a two dimensional scattering model to a three dimensional problem, and (3) developing some initial results with incorporating foliage effects in the model. The second phase of this research covered the measurement of various modes of near earth propagation including line of sight, shadowed line of sight, diffraction by both smooth and forested hills, and a long (25 km) occluded paths. The measurements were accomplished with a team comprising Wes Sizemore (NRAO-GB), Bruce Naley (NSWC-DD), Earnest Chilton (NSWC-DD), and other helpers from NSWC-DD. All measurements were accomplished by placing a receiver on the Jansky Laboratory roof (near to and above the Control Center) and locating a transmitter at various remote sites representing the path conditions noted above. Signal strength measurements under low and moderate wind conditions and both vertical and horizontal polarizations were acquired when the Green Bank Telescope was down for maintenance. Relatively high gain, narrow beamwidth antennas were employed where possible to minimize the out of plane terrain scattering effects.

The analysis phase comprised (1) incorporating cable loss and antenna gain calibrations in the links equations, (2) comparisons between various forms of the model and data, and (3) limited work with some very approximate foliage propagation characterization. The agreement between the measurements and the various models will be presented and discussed. In general, the agreement was good but there were exceptions especially when dealing with mid-path diffraction by a foliage covered mountain and fairly windy conditions. Finally, some suggestions for further analysis and measurements will be presented.

By: Yuri Kovalev (ASC Lebedev)

I will present in the talk first scientific results of the Space VLBI project RadioAstron on quasars, pulsars, ISM, and galactic masers which have by far exceeded our expectations and provided solid basis for implementation of the open key science program of the mission.

By: Peter Martin (CITA)

By virtue of its multi-frequency all-sky mapping to probe the CMB, Planck has also produced marvelous maps of the foreground emission from the Galaxy, with unprecedented sensitivity and resolution. I will present highlights of what we are learning about thermal dust emission, including its polarization, anomalous microwave emission, and CO.

By: Jay Lockman (NRAO, Green Bank)

This talk will review some of the discoveries that have been made in recent years using the Green Bank Telescope.  I will cover the solar system, including the spin of Mercury and volcanoes on Venus; insights into the formation of stars; discovery of complex molecules in interstellar space and their possible connection to life on Earth; the structure and evolution of the Milky Way and nearby galaxies; and many other topics. The talk is aimed at a general audience with some scientific interest but no particular expertise in astronomy.

By: Mark Devlin (University of Pennsylvania)

Clusters of Galaxies are the largest gravitationally-bound objects in the Universe. They form via mergers with energetics that are only rivaled by the Big Bang. The study of these objects and collisions can reveal the complex processes that govern the interactions. Observations at 90 GHz with the MUSTANG instrument on the GBT provide high (9”) resolution of the Sunyaev-Zel’dovich effect inside the clusters. Initial observations with the MUSTANG instrument have yielded very promising observations of a few clusters. We are now in the midst of an upgrade which will allow us to observe hundreds of clusters (assuming we can keep the GBT open!!!!).

Gail Zasowski, Johns Hopkins University

One of the longest standing puzzles of galactic astronomy and astrochemistry is the nature of the Diffuse Interstellar Bands (DIBs).  These seemingly ubiquitous ISM absorption features are seen superimposed on the spectra of stars, galaxies, and quasars, but despite nearly a century of study, no physical carrier has been positively identified.  The vast majority of our knowledge of DIBs is from optical data, as the first near-IR H-band features, detected towards a handful of stars, were not published until 2011.  I will describe a new project that increases the number of these detections by orders of magnitude and, contrary to most DIB studies to date, characterizes them to use as tools for understanding the Galactic ISM on large scales.  The dataset comprises high resolution, H-band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE, part of the SDSS-III), which takes advantage of the reduced effects of extinction at IR wavelengths to probe stars throughout the Galactic bulge, disk, and halo, homogeneously sampling a wide range of ISM environment.  I will discuss how this catalog of near-IR DIBs is being used to map the DIB carrier's distribution within the Milky Way and to relate it to other Galactic ISM tracers.  I will also present new statistical analyses of quasar and galaxy spectra that probe weak,  high-latitude optical DIBs.  These analyses demonstrate the power of large datasets to provide new insights into the properties of these poorly-understood feature carriers and the ISM in which they reside.

Kristen McQuinn (University of Minnesota)

Starbursts are short-lived periods of intense star formation whose energy output dominates the total luminosity of their host galaxies. The ionizing radiation, mass loss, and nucleosynthesis of the massive stellar populations formed in a burst can alter the gas dynamics, future star formation, and chemical composition of the host galaxy. Local starbursts (z << 1) provide 10% of the radiant energy production and ~20% of all the high mass star formation (e.g., Heckman et al. 1998; Brinchmann et al. 2004). Among the many morphological types in which starbursts have been seen, dwarf galaxies offer valuable laboratories in which to study the starburst phenomenon. As part of a multi-wavelength study, new and archival observations of x-ray, ultraviolet, optical, Halpha, infrared, and HI emission are being combined to create a holistic picture of the starburst phenomenon in the nearby dwarf galaxies. In this talk, I will discuss recent results quantifying both the temporal and spatial characteristics of the starburst phenomenon from star formation histories reconstructed from the optically resolved stellar populations. I will also highlight ongoing work to measure the evolutionary impact of starbursts through galactic outflows and, with a new GBT program, search for evidence of galaxy interactions as the trigger mechanism of the starbursts.

By: Matthew Walker

I will discuss efforts to use the motions of stars to learn about the nature of particles. More specifically, I will translate stellar kinematics observed in the nearest, smallest and and 'darkest' galaxies into a test of the standard hypthesis that dark matter consists of 'cold' and 'collisionless' (i.e., weakly interacting) particles. This model now seems to require that baryon-driven processes (e.g., energetic feedback from supernova explosions) alters the internal structure of galactic dark matter halos systematically with respect to predictions derived from dissipationless cosmological simulations. I will discuss future work that will let us judge whether such reconciliation is energetically feasible or whether the dark matter model requires more complexity.

In this talk, we will discuss research activities in the Department of Computer Science and Electrical Engineering (CSEE) at West Virginia University (WVU) that may be of interest to researchers and staff at NRAO.  These activities include video and image processing, wireless communications and networking, and statistical signal processing, e.g., target tracking.  We will also discuss, in more detail, results from a NSF-funded project dealing with wireless networks that are supplemented by non-broadcast links.  The motivation behind this research includes recent results showing that for purely wireless networks, per-node throughput goes to zero networks get large.  The problem appears to be physical in nature, i.e., space itself is a capacity-bearing object.  Our approach, which we call multimodal networking, is joint optimization of all communication modes available, including broadcast wireless and any non-broadcast or wired modes.  We contrast this approach with conventional infrastructure-aided networking, e.g., cellular networks, and we provide achievable rates, power optimization, and information outage probabilities for Gaussian networks.  We will conclude by discussing NRAO-CSEE collaboration ideas and plans for future interactions

By Jon Romney (NRAO-Socorro)

By Ann Mao (University of Wisconsin)

Radio polarimetry, particularly across a wide band, is a truly unique probe of the magnetized medium in galaxies. It can be used to derive large-scale magnetic field structures as well as turbulent properties. In this talk, I will present the latest Jansky Very Large Array polarization observations of the Whirlpool galaxy and what they tell us about the large-scale magnetic fields and turbulence in its halo. In addition, I will describe on-going efforts to measure magnetic fields in HVCs and in galaxies at "higher" redshift.

by Jean-Luc Margot (UCLA)

By Neal Erickson (UMass-Amherst)

UMass and BYU are building a 64 element phased array receiver for use in the focal plane of the GBT, in the frequency range 70-95 GHz. These receivers offer the potential to synthesize up to four times more beams than there are elements, and to measure and correct large scale telescope surface errors.  There are many unique challenges with building such a receiver at short wavelengths, and in applying it at the Gregorian focus.

The talk will discuss the theory of beamforming with the array and the results of simulations of feed efficiency.  This receiver uses cryogenic MMIC amplifiers in the front end followed by room temperature amplification and mixing, requiring several innovations in construction.

These unique features will be described, as well as the layout of the backend beam summing and calibration network.

By David Thilker

Due to recent wide-area surveys conducted by GALEX, Pan-STARRS1, and WISE, plus targeted observations by HST, our generation is afforded the remarkable opportunity to accomplish panchromatic dissection of unprecedented numbers of galaxies in the local universe, even at the scale of individual stars in the nearest objects. Such results may be compared against the emerging view of predecessor objects at high redshift. The broad wavelength coverage of space-based surveys allows the substructure of nearby galaxies to be interpreted meaningfully in terms of realistically complex stellar populations while allowing robust correction for dust obscuration. We will demonstrate our innovative approach to generating a more comprehensive, physically-interpreted view of z ~ 0 galaxy structure via pixel-SED fitting of resolved galaxies. To accomplish such data processing, we have created a successful distributed computing network, enabled by volunteer citizen scientists. Our early work has been focused on visible-light observations from Pan-STARRS1 and SDSS, but we are now in the process of broadening our spectral scope over the UV-IR domain. For thousands of galaxies, we will determine maps of key physical parameters based on UV-IR pixel-SED fitting. We will compute the entire suite of CAS+Gini+M_20 non-parametric morphology indicators from the resulting images of stellar mass (M*) and extinction-free star formation rate (SFR). Further, parametric models of galaxy structure (bulge, disk, bar) will be derived directly using the stellar mass maps. Our overarching science goal is understanding the evolution of galaxies with respect to their position and trajectory in the global (M*, SFR) plane, using maximally orthogonal, quantitative measures of stellar structure and SF modes obtained from our physical parameter maps. We now quantify the z~0 view, but envision that our pixel-SED fitting resource can later be applied to galaxy populations at moderate (LSST+WFIRST) and high z (CANDELS, Frontier fields), even if rest-frame IR bands are unavailable in that case. If time permits, we will provide a brief overview of LEGUS, the Legacy ExtraGalactic UV Survey, which is complementary to our pixel-SED fitting in the sense that it links the ~kpc scale results of our investigation to the constituent stars and clusters at the start of the SF hierarchy.

By Dr Dror Baron – NC State University


Traditional signal acquisition techniques sample band-limited analog signals above the Nyquist rate. Compressed sensing (CS) is based on the revelation that a sparse signal can be reconstructed from a small number of linear projections of the signal. Therefore, CS-based techniques can sample sparse signals at sub-Nyquist rates. Potential applications include broadband analog-to-digital conversion and new kinds of imaging devices.
The focus of our recent research has been on CS algorithms that can reconstruct signals despite not knowing their statistical properties. We will describe algorithms that are universal in the sense that they can adapt to unknown statistics. We will conclude the talk by briefly surveying recent work on a fast parallel algorithm for data compression, which can be used in applications involving high data rates including lossless compression of radio astronomy data.

By: Kevin Bandura (McGill University)

Dark Energy is arguably the greatest mystery in science today.  A promising technique in the pursuit of unraveling the mystery of Dark Energy is 21cm intensity mapping observations. I will discuss observational and instrumentation advances to date.  In particular I will introduce the Canadian Hydrogen Intensity Mapping Experiment (CHIME currently under construction at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC. I will detail the novel telescope design concept, details about the correlator, and the current commissioning of the 1/10th scale CHIME pathfinder.