Oral Presentation Abstracts

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Saturday, January 15, 2011

Michael Kaufman (San Jose State University)

The Atomic Universe: Emission from Gas in the Ionized, Diffuse and Dense ISM  (Invited talk)  (withdrawn)

Atoms in the interstellar medium emit line radiation when exposed to UV radiation from stars. The processes that convert UV to line radiation depend on the particular interstellar environment, and as a result the line emission has great diagnostic value. Interpretation of the emission lines can be used to measure gas temperature, density, strength of the local ultraviolet field and metallicity. In this talk, I will review the physical processes that give rise to important line emission from dense and diffuse neutral (HI) clouds exposed to Far-Ultraviolet (FUV) radiation, as well as from ionized (HII) gas. The diagnostic value of such species as [CII], [OI], [SiII], [NII] and [FeII] will be emphasized. Applications include interpreting emission from individual diffuse cloud components and dense star forming regions in the Milky Way, to massive star forming regions in starburst galaxies and the energetic ISM of high-redshift quasars. ALMA's high spatial resolution and sensitivity make it the ideal facility for studying atomic gas near and far.

Gordon Stacey (Cornell University)

Carl Ferkinhoff (Cornell University)
Thomas Nikola (Cornell University)
Steve Hailey-Dunsheath (MPE, Garching)
Johannes Staguhn (Johns Hopkins, GSFC)
Dominic Benford (GSFC)

Far-IR Fine-structure Line Emission from High Redshift Galaxies

Using our submillimeter grating spectrometer ZEUS on the CSO we have detected the 158 μm [CII] line from a group of 13 galaxies in the redshift interval from 1 to 2, and the 88 μm [OIII] line from two galaxies at z = 2.8 and 3.9. These lines are important cooling lines for the neutral and ionized ISM in galaxies, and trace the physical conditions of the gas and strength and hardness of the local UV radiation fields. The redshift 1 to 4 interval covers the peak epoch for star formation per unit volume in the universe, and we will discuss the results of our survey and the implications for star formation and its relationship to AGN activity in the early Universe. We will also discuss the utility of the ensemble of bright far-IR fine-structure lines ([CII],[OI],[OIII],[NII],[NIII]) as diagnostics of the age, intensity and spatial extent of star formation at high redshift. We include methods for determining the origins of these lines (AGN and star formation?), and finish with a discussion of the new opportunities opened up with ALMA.

Hsien Shang (ASIAA)

Al Glassgold (UC Berkeley)
Wei-Chieh Lin (ASIAA)
Chun-Fan Liu (ASIAA)

Ne II Fine-structure Line Emission from the Outflows of Young Stellar Objects

The flux and line shape of the fine-structure transitions of Ne II and Ne III at 12.8 and 15.55 μm and of the forbidden transitions of O I 6300 are calculated for young stellar objects with a range of mass-loss rates and X-ray luminosities using the X-wind model of jets and the associated wide-angle winds. For moderate and high accretion rates, the calculated Ne II line luminosity is comparable to or much larger than produced in X-ray irradiated disk models. All of the line luminosities correlate well with the main parameter in the X-wind model, the mass-loss rate, and also with the assumed X-ray luminosity and with one another. The line shapes of an approaching jet are broad and have strong blue-shifted peaks near the effective terminal velocity of the jet. They serve as a characteristic and testable aspect of jet production of the neon fine-structure lines and the O I forbidden transitions.

Jeff Wagg (ESO, Santiago)

Prospects for studies of the interstellar gas in high-redshift galaxies

The submm/mm-wavelength sensitivity of ALMA will bring about a revolution in our understanding of both the atomic and molecular interstellar medium (ISM) in high-redshift galaxies. Up to recently, studies of the cool gas in massive objects at earlier Cosmic times have mainly focused on observations of redshifted molecular CO line emission, a robust tracer of the total molecular gas available for fueling star-formation and AGN activity, as well as a tracer of the dynamical mass. However, the main cooling line in the ISM of star-forming galaxies is the 157.7 μm [CII] emission line, redshifted to favourable atmospheric windows for galaxies at z>1. In this talk, I will present recent results related to the study of [CII] line emission at high-redshift, and discuss the prospects for ALMA studies of this line out to the epoch of reionization at z>6.

Ilse De Looze (University of Ghent)

Maarten Baes (Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, S9, B-9000 Gent, Belgium)
George J. Bendo (Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK )
Luca Cortese (European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching bei Muenchen, Germany)
Jacopo Fritz (Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, S9, B-9000 Gent, Belgium)

The reliability of [CII] as a SFR indicator

The [CII] line at 158μm is an important coolant for the neutral interstellar gas. Since it generally is a very strong line in all star forming galaxies, [CII] is also a potentially powerful tracer of star formation activity. In order to examine the reliability of [CII] as a diagnostic for the star formation rate (SFR), we calibrated a SFR relation for a sample of 24 star forming late-type galaxies in the nearby universe. For this calibration, we rely on GALEX FUV data, an ideal tracer of unobscured star formation, and both MIPS 24 µm and IRAS data, to probe the dust-enshrouded fraction of star formation. Unlike previous SFR calibrations, we find that the SFR correlates well with the [CII] luminosity, indicating that the [CII] luminosity is a reliable SFR indicator. Besides a quantative SFR calibration, the tightness of this relation also gives us insight in the origin of the [CII] emission on a global galaxy scale.

Considering the comparable [CII] luminosities for galaxies at z = 1-2 and the enhanced [CII] emission at even higher redshift compared to local galaxies with similar FIR luminosities, the applicability of such a SFR relation will be immense in future high redshift surveys (both with Herschel and ALMA).

B-G Andersson (SOFIA/USRA)

Ravi Sankrit (SOFIA/USRA)
The SOFIA Science Team

SOFIA and ALMA - a powerful combination

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is now performing scientific observations and the Announcement for Opportunity (AO) for the second-generation instruments is about to be released. SOFIA covers a broad wavelength range from the visual to sub-mm wavelengths with a focus on the Mid- to Far-Infrared. It has a long lifetime and spatial resolution comparable to ALMA in its compact 150m configuration. Current and expected SOFIA instruments provide many synergies between ALMA and SOFIA. For instance, SOFIA's heterodyne spectrometers will probe Far-infrared (FIR; nu > 1 THz) lines, including [O I], [C II] and [N II] and many hydrides, at high spectral resolution. Echelle spectroscopy in the Mid-infrared (MIR) similarly will allow observations of e.g. fine-structure lines, warm water and H2 pure rotational lines. Together, these will complement ALMA's broad spectral coverage of molecular lines in the nu > 1 THz range, for addressing questions of interstellar chemistry and physics in star forming regions, PDRs and galaxies. Mid-infrared (MIR) grism spectroscopy, of e.g. dust and ices, can be combined with ALMA spectroscopy of the freeze-out of molecules from the gas phase to better understand the formation, destruction and characteristics of interstellar ices. Imaging in the MIR and FIR and FIR polarimetry can be combined with ALMA (sub-)mm wave observations to provide a more complete picture of the temperature, density and magnetic field structure of e.g. star forming cores. The combination of ALMA and SOFIA thus will provide long-term access to a broad range of tracers of the chemistry and physics of the ISM, star formation and galaxy evolution. We will highlight the current and expected capabilities of SOFIA and some of the expected synergistic capabilities with ALMA.

Edwin A. Bergin (University of Michigan)

The Spectral World Beyond Carbon Monoxide  (Invited talk)

ALMA will open up new avenues of exploration encompassing the wide range of star formation in our galaxy and peering into the central heart of planet-forming circumstellar disks. As we seek to explore the origins of stars and planets molecular emission will be at the front and center of many studies probing gas physics and chemistry. In this talk I will review of the state of the field of molecular spectroscopy from the beginnings of stellar birth and onwards to the formation of planets. From existing observations of star-forming regions we observe a large degree of chemical complexity within cold pre-stellar cores and extending towards massive cluster-forming clumps. This issue will become more acute with the greater sensitivity and resolution of ALMA. I will discuss how this complexity hides clues towards molecular origins, but also provides a unique tool to isolate disparate regions and paint a more complete physical picture of the object. I will end with a discussion of one of the major new ALMA frontiers: the ability to probe the planet-forming zones of circumstellar disks. I will outline how we can use this new capability to study the origins of terrestrial and giant planets along with the overall evolution of the gas inside protoplanetary disks. As we enter this new exiting era we will all discover the rich spectral world beyond CO.

Crystal Brogan (National Radio Astronomy Observatory)

Todd Hunter (NRAO)
Claudia Cyganowski (CfA)
Claire Chandler (NRAO)
Remy Indebetouw (UVa/NRAO)
Rachel Friesen (NRAO)

An EVLA Diagnostic K-Band Survey of Massive Young (Proto)stellar Objects

We will present early results from a comprehensive study of 25 massive young stellar objects (MYSOs) at 24 GHz (13mm) utilizing the power of the new EVLA WIDAR correlator to simultaneously observe the ammonia ladder through (6,6), the 25 GHz methanol ladder, SO2, HC5N, recombination lines, and continuum at a spatial resolution of ~ 10,000 AU. The selection criteria included: previous ammonia detections at (1,1) and (2,2), (sub)mm dust cores, a range of maser activity, and a range of 24 micron luminosities and 8/24 micron colors. Together, the observed tracers provide the gas temperature, the frequency and strength of hot core emission, and the kinematics of cores, outflows, and ionized gas, all observed with a uniform sensitivity and resolution. With this wealth of data we aim to identify the best discriminators of MYSO evolutionary state, and ultimately better understand the process of massive star formation.

Karin Oberg (Harvard-Smithsonian Center for Astrophysics)

Chunhua Qi (Harvard-Smithsonian CfA)
Brian Svoboda (Western Washington University)
Jeffrey Fogel (University of Michigan)
Edwin Bergin (University of Michigan)
David Wilner (Harvard-Smithsonian CfA)

DISCS: A spatially and spectrally resolved survey of chemistry in protoplanetary disks

Molecular abundances in protoplanetary disks provide important clues to the chemical evolution and the physical conditions prevalent during star- and planet-formation. The aim of DISCS (Disk Imaging Survey of Chemistry with the SMA) is to constrain the impact of the disk physics on the disk chemistry through a homogeneous survey of spatially and spectrally resolved line emission of 8 key molecules and ions -- CO, HCO+, DCO+, N2H+, HCN, DCN, CN, H2CO -- in 12 protoplanetary disks using the Submillimeter Array. A range of physical disk environments is ensured by including sources that span stellar spectral types from M1 to A0, orders of magnitude different accretion luminosities and X-ray fluxes, and that exhibit the full range of grain evolution parameters found in disks. Considering this range of radiation environments, we find a surprisingly small variation in the proposed radiation tracer CN/HCN across the sample. We detect an equally surprisingly high variation in the ratio of the cold chemistry tracers DCO+ and N2H+, which has inspired our first model efforts. Building on the DISCS results, I will end with some thoughts on what immediate progress ALMA can provide in our understanding of protoplanetary disk chemistry.

David Meier (New Mexico Tech)

Jean Turner (UCLA)
Anthony Remijan (NRAO - CV)

High Resolution Gas Chemistry in Strong Starburst Galaxies (withdrawn)

Strong starbursts represent some of the most extreme molecular environments in the local universe. Their large molecular columns, intense radiation fields and disturbed morphologies must influence the evolution of star formation. Gas chemistry evolves in step with the evolving interstellar medium (ISM) making it a powerful probe of the structure of the ISM. We have surveyed several nearby strong starbursts, including M 82, one of the nearest LIRGs, IRAS 04296+2923, and the nearest ULIRG, Arp 220, in a collection of astrochemically important species with the CARMA array. We discuss high spatial resolution maps of shock tracers (CH3OH, SiO, and HNCO), photon dominated region (PDR) tracers (C2H and CN) and dense, quiescent gas tracers (N2H+) in these galaxies and compare them to more 'normal' systems. The chemical differentiation seen in GMCs of nearby 'normal' nuclei is observed to persist to the kiloparsec scales. In IRAS 04296+2923 intense nuclear star formation is driven by a strong, young bar, apparent in the shock tracers. PDR chemistry is tightly confined to the burst region, making its chemistry appear as a scaled up version of nearby 'normal' galaxies hosting nuclear bars. In Arp 220, shocks arise primarily between the two nuclei. The extended disk is also the site of PDR emission in C2H. The abundance of C2H is found to be lower than expected based on extrapolations of M 82. Evidently C2H abundances exhibit a similar "deficit" seen in C+, suggesting the deficit is propagated to its molecular daughter species. Possibilities of using C2H as a proxy for imaging [CII] at arcsecond resolution are discussed in light of new Herschel results.

Amanda Heiderman (University of Texas at Austin)

Neal Evans (University of Texas at Austin)
Lori Allen (National Optical Astronomy Observatory)
Tracy Huard (University of Maryland)
Mark Heyer (University of Massachusetts)

The Star Formation Rate and Gas Surface Density Relation in the Milky Way: Implications for Extragalactic Studies

We investigate the relation between star formation rate (SFR) and gas surface densities in Galactic star forming regions using a sample of young stellar objects (YSOs) and massive dense clumps. Our YSO sample consists of objects located in 20 large molecular clouds from the Spitzer cores to disks (c2d) and Gould's Belt (GB) surveys. These data allow us to probe the regime of low-mass star formation essentially invisible to tracers of high-mass star formation used to establish extragalactic SFR-gas relations. We estimate the gas surface density (Sigmagas) from extinction (Av) maps and YSO SFR surface densities (SigmaSFR) from the number of YSOs, assuming a mean mass and lifetime. We also divide the clouds into evenly spaced contour levels of Av, counting only Class I and Flat SED YSOs, which have not yet migrated from their birthplace. For a sample of massive star forming clumps, we derive SFRs from the total infrared luminosity and use HCN gas maps to estimate gas surface densities. We find that c2d and GB clouds lie above the extragalactic SFR-gas relations (e.g., Kennicutt--Schmidt Law) by factors up to 17. Cloud regions with high Sigmagas lie above extragalactic relations up to a factor of 54 and overlap with high-mass star forming regions. We use 12CO and 13CO gas maps of the Perseus and Ophiuchus clouds from the COMPLETE survey to estimate gas surface densities and compare to measurements from Av maps. We find that 13CO, with the standard conversions to total gas, underestimates the Av-based mass by factors of ~4-5. 12CO may underestimate the total gas mass at Sigmagas ~200 Msol pc-2 by >~30%; however, this small difference in mass estimates does not explain the large discrepancy between Galactic and extragalactic relations. We find evidence for a threshold of star formation (Sigmath) at 129+/-14 Msol pc-2. At Sigmagas  > Sigmath, the Galactic SFR-gas relation is linear. A possible reason for the difference between Galactic and extragalactic relations is that much of Sigmagas is below Sigmath in extragalactic studies, which detect all the CO-emitting gas. If the Kennicutt--Schmidt relation (SigmaSFR > Sigmagas1.4) and a linear relation between dense gas and star formation is assumed, the fraction of dense star forming gas (fdense) increases as ~Sigmagas0.4. When Sigmagas reaches ~300Sigmath, the fraction of dense gas is ~1, creating a maximal starburst.

Richard Crutcher (University of Illinois)

Understanding the Role of Magnetic Fields in Star Formation - ALMA Spectropolarimetry

The role of magnetic fields in all aspects of star formation -- molecular cloud formation, fragmentation, contraction, formation of disks and protostars, and generation of bipolar outflows -- remains unclear. The best and perhaps the only way to resolve the controversy about what drives the star formation process is to observe magnetic fields and compare the results with theoretical predictions. Of the three available techniques, (1) linearly polarized dust emission, (2) Zeeman splitting of molecular lines, and (3) linearly polarized molecular lines (Goldreich-Kylafis or GK effect), two involve spectropolarimetry. In this talk I briefly describe the power and limitations of mm-line spectropolarimetry, summarize current results, and discuss the advances that may be expected with ALMA. To date the Zeeman effect has been detected in the 3-mm lines of CN and C2H with the IRAM 30-m telescope, providing information about line-of-sight magnetic field strengths in regions with n(H2) ~ 104-6 cm-3, but with angular resolution ~25". CARMA observations have shown that CN at least is not interferometrically resolved out at ~2" resolution. ALMA mapping of the Zeeman effect in molecular spectral lines will make it possible to map the line-of-sight magnetic field strength in molecular clouds and cores. This will enable study of possible changes with radius in mass/magnetic flux ratios (M/Phi) on the scale of molecular cores in order to test strong-field star formation theory. In particular, ambipolar-diffusion driven star formation makes a specific prediction that M/Phi must increase with decreasing radius; ALMA should be able to test this prediction on the scale of protostellar cores and their envelopes. The GK effect in CO is the best available technique for study of magnetic field morphology in outflows, and ALMA mapping will have sufficient resolution and sensitivity to study this magnetically-driven process. The GK effect may also be mapped in molecular cores using various molecular species and transitions, which are sensitive to different H2 densities and line optical depths. It should be possible to obtain maps of magnetic field morphology in "onion-ring like" shells of molecular cores. The wealth of spectropolarimetry (and continuum polarimetry) data will enable comparisons of computer simulations of molecular clouds and cores. The simulations can be ``observed'' with the ALMA instrumental signature to produce Stokes I, Q, U, V maps for direct comparison with ALMA observations, in order to obtain the best possible models of the 3D magnetic vector B in molecular clouds. ALMA will provide unprecedented sensitivity and resolution for the measurement of magnetic field strength and morphology, and will significantly advance our understanding of the role of magnetic fields in molecular cloud evolution and star formation.

Lewis B. G. Knee (ALMA)

From AIV to Early Science: an ALMA Progress Report

Over the past three years, ALMA has progressed from the acceptance of the first antennas operating as single-dish instruments at the OSF, to a multi-element imaging array operating at the AOS. In this presentation I will review the progress in the construction and commissioning of the array, describe the intended capabilities for Early Science, and present examples of the spectroscopic and continuum images currently being produced as part of the commissioning and science verification phase.

Sunday, January 16, 2011

Chris Wilson (McMaster University)

Molecular Spectroscopy of Galaxies  (Invited talk)

Spectroscopic observations of other galaxies allow us to probe a wider range of physical and chemical environments than is available within our own Galaxy. I will review recent observations of nearby galaxies which are revealing a surprising chemical complexity in starburst and ultraluminous infrared galaxies. I will also discuss what we have learned about the molecular gas content in nearby normal galaxies and star forming galaxies at high redshift from recent large CO surveys.

Wayne Schlingman (University of Arizona)

Yancy L. Shirley (University of Arizona)
David E. Bolin (University of Arizona)
Erik Rosolowsky (University of British Columbia, Okanagan)
John Bally (University of Colorado)
The Bolocam Galactic Plane Survey Team

The Bolocam Galactic Plane Survey V: HCO+ and N2H+ Spectroscopy of 1.1 mm Sources

We present the results of observations of 1882 sources in the Bolocam Galactic Plane Survey (BGPS) at 1.1~mm with the 10m Henrich Hertz Telescope simultaneously in HCO+ J=3-2  and N2H+ K=3-2. We detect 77% of these sources in HCO+ and 51% in N2H+ at greater than 3sigma. We find a strong correlation between the integrated intensity of both dense gas tracers and the 1.1 mm dust emission of BGPS sources. We determine kinematic distances and break the distance ambiguity for 648 sources (537 in the first quadrant and 111 in the second quadrant) for which we derive the size, mass, and average density. The median size of BGPS clumps is 0.75 pc with a median mass of 330 Msol (assuming Tdust = 20K). The median HCO+ linewidth is 2.9 km/s indicating that BGPS clumps are dominated by supersonic turbulence or unresolved kinematic motions. We find no evidence for a size-linewidth relationship for BGPS clumps. We analyze the effects of the assumed dust temperature on the derived clump properties with a Monte Carlo simulation and we find that changing the temperature distribution will change the median source properties (mass, number density, surface density) by factors of a few. The observed differential mass distribution has a power-law slope that is intermediate between that observed for diffuse CO clouds and the stellar IMF. BGPS clumps represent a wide range of objects (from dense cores to more diffuse clumps) and are typically characterized by larger sizes and lower densities than previously published surveys of high-mass star-forming regions. This collection of objects is a less-biased sample of star-forming regions in the Milky Way that likely span a wide range of evolutionary states.

Maryvonne Gerin (LERMA)

Pety J (IRAM)
Falgarone E (LERMA)
Lis D. (CalTech)
Neufeld D. (JHU)
Persson C. (Chalmers)

Absorption spectroscopy with Herschel/HIFI and PdBI : promises for ALMA

We present results of absorption spectroscopy of simple interstellar molecules obtained with Herschel/HIFI and IRAM-PdBI towards massive star forming regions. The Herschel/HIFI data give access with unprecedented sensitivity to interstellar hydride line profiles (CH, CH+, OH+, H2O+, H3O+, H2O, NH, NH2, NH3, HF, SH+), while the complementary PdBI data allow us to probe the spatial structure of the absorption features across the background source millimeter continuum emission. We discuss how these observations lead to a renovated understanding of the properties of the diffuse interstellar medium, and the new diagnostic possibilities offered by interstellar hydride lines. We show examples of observation programs that could be carried on with ALMA, from the local universe to the most distant galaxies.

Alison Crocker (University of Massachusetts Amherst )

Melanie Krips (IRAM Grenoble)
Martin Bureau (University of Oxford)
Timothy Davis (University of Oxford)
Katey Alatalo (University of California Berkeley)
Atlas3D Team

Molecular gas properties of early-type galaxies

Surveys now show that a significant fraction (approximately one quarter) of early-type galaxies have molecular gas, detected via 12CO. The molecular gas in early-types is found to be in very central distributions, where the effects of shear, hydrostatic pressure and possible AGN influence will be maximal. But little is yet known about the state of molecular gas in these galaxies. I will present the results of a survey of 18 molecular-gas rich early-type galaxies from the Atlas3d sample in 12CO13CO, HCN and HCO+ from the IRAM 30m telescope. This study reveals a wide range of average optical depths for the molecular gas with some galaxies having 12CO/13CO ratios similar to individual Galactic molecular clouds and some with much higher ratios, as seen in starburst systems. The HCN/13CO ratios, measuring dense gas fraction, have a smaller range and resemble those seen in spirals. Despite the very central distribution of gas, early-type galaxies do not have the high dense gas fractions of starbursts. Interestingly, some of the molecular gas properties correlate with galaxy mass. Massive galaxies tend to be most deficient in 12CO, relative to the other tracers. These are also the galaxies with the lowest dust temperatures and high molecular to atomic gas ratios. These may be galaxies undergoing 'morphological quenching' with lower than normal star-formation efficiencies given their molecular gas masses. Detailed studies of the star formation in these systems are required to confirm this hypothesis.

Lauren Cleeves (University of Michigan)

Edwin A. Bergin (University of Michigan)
Jeffrey K. J. Fogel (University of Michigan)
Nuria Calvet (University of Michigan)
Thomas J. Bethell (University of Michigan)

Transition disk chemistry in the eye of ALMA

One of the more exciting results from Spitzer surveys of young star-disk systems was the detection of so-called transition disks [1,2]. These systems appear to have opacity ``holes'' in the inner disk (from a few to tens of AU) that may be the result of planet-formation and inner disk clearing at one million years [3]. Curiously transition disks stand out in the handful of systems observed to have rich gas-disk chemistry in the outer disk with detections of a variety of molecules such as HCO+, CN, and HCN [4]. Consequently these transition disk systems are very well suited towards ALMA's high resolution and spectral sensitivity, which will allow us to probe these disks' chemical structure in great detail. However, to fully understand such complex environments detailed disk chemical modeling is necessary. Using a Monte Carlo radiative transfer code for the UV continuum along with an added treatment for Ly-alpha within a comprehensive disk chemical model [5], we explore the chemical nature of a variety of transition disk systems at different evolutionary stages. For this presentation, I outline features of this model along with recent results and the predicted ALMA observed emission. The primary result shows that transition systems are fertile ground for study with ALMA as the gap edge ``lights-up'' in emission from molecular species, including CO, HCN, and H2CO, that otherwise would not be present at such large distances from the star. This is crucial because it is generally difficult to observe the midplane in molecular emission because of freeze-out. In these systems the hidden midplane becomes revealed and the gas physics/chemistry can be studied with many molecular transitions that trace the gap edges and the outer disk surface. It is clear that ALMA will unlock the ability to study the initial stages of planet formation inside gas-rich disks, and this presentation will highlight the unique aspects offered by observations of transition disks with ALMA.
1. Espaillat et al. 2010, ApJ, 717, 441.
3. Cieza et al. 2010, ApJ, 712, 925.
3. Rice et al. 2003, MNRAS, 342, 79.
4. Öberg et al. 2010, ApJ, 720, 480.
5. Fogel et al. 2010, ApJ, Accepted.

Stefanie Milam
(NASA Goddard Space Flight Center)

Anticipated Advances in Astrobiology with ALMA  (Invited talk)

There have been extensive searches for prebiotic molecules in the interstellar medium, such as amino acids, nucleic acid base structures, and complex sugars (e.g. Kuan et al. 2003; Snyder et al. 2005; Charnley et al. 2005; Apponi et al. 2006; Hollis et al. 2000). The formation mechanisms of these species are uncertain, though they are generally considered to be, at least in part, the products of solid phase chemistry. Smaller organics likely essential for their formation, such as H2CO, NH3, CH3OH, and HCN, freeze onto the surfaces of dust grains in cold dense environments, where they may react with other condensates or become exposed to an external radiation source forming new molecules and radicals that eventually sublime from grain surfaces. Extensive laboratory studies have been conducted to gain a further understanding of the formation for these biomolecules in interstellar conditions, both in the gas phase and solid phase. Large organics tend to have fairly elaborate spectra (i.e. large partition functions and large rotational constants) that makes conclusive identifications difficult. Additionally, these molecules are typically associated with regions of complex chemistry with numerous known species and a near equal amount of unidentified transitions, creating a forest of lines often at the confusion limit. As such, the search for many of these complex prebiotics that have been sought for have proven unsuccessful. ALMA's exceptional sensitivity, large spectral bandwidth, high spectral resolution, and angular resolution (down to 10 milliarcsec) will enable researchers for the first time to better resolve the compact emission regions of complex biomolecules while obtaining nearly 8 GHz of instantaneous bandwidth to fully characterize their spectrum. In addition, the spatial information and line profiles can be obtained over 800 GHz of bandwidth in 8 receiver bands to not only assist in the identification and source of spectral lines and emission components for a given species but also to help elucidate the chemistry of prebiotic species.
Apponi, A.J. et al. 2006, ApJ, 652, 1787
Charnley, S.B. et al. 2005, AdSpR, 36, 132
Hollis, J.M. et al. 2000, ApJ, 540, L107
Kuan, Y.-J. et al. 2003, ApJ, 593, 848
Snyder, L.E., et al. 2005, ApJ, 619, 914

Robin Garrod (Cornell University)

Tyler Pauly (Iowa State University)

Modeling the formation of interstellar CO2, CO and water ice

Observations of interstellar dust-grain ices indicate the presence of a selection of simple molecules, including H2O, CO and CO2. Of these, CO2 and water are believed to form primarily on the dust grains themselves, while CO is accreted directly from the gas phase. Water and CO2 ices have been detected along lines of sight with relatively low visual extinction (3--4 magnitudes in Taurus); however, the threshold for CO2 detection is significantly greater (~7 magnitudes). Since CO is required for the grain-surface formation of CO2, the efficiency of CO to CO2 conversion must vary over this range of extinctions. However, the precise mechanism of grain-surface CO2 formation is uncertain, and previous models have been unable to reproduce observed CO2 abundances, nor the correct threshold visual extinction.

I will present the results of a new, detailed gas-grain chemical model of a quiescent molecular cloud. This model allows the individual layers of ice to be resolved, allowing the chemical composition and ``polar properties'' (i.e. H2O content) to be traced within each ice layer. I will show that the use of a more physically accurate model of surface chemistry and ice structure allows the observed CO2 ice abundance to be well reproduced, using uncontroversial reaction mechanisms. The observed threshold visual extinctions of H2O, CO and CO2 are also reproduced with this method, with the precise values largely dependent on gas density. I will show how the observed sequence of interstellar ice deposition (H2O ... CO2 ... CO) may be understood through a combination of chemical and physical influences. I will also consider the related behavior of ice species such as methanol (CH3OH), which provides molecular material for the later formation of much more complex molecules during star formation.

Colette Salyk (University of Texas McDonald Observatory )

Klaus Pontoppidan (Space Telescope Science Institute)
Geoffrey A. Blake (California Institute of Technology)
Joan Najita (NOAO)
John Carr (Naval Research Laboratory)

Observations of water in circumstellar disks

Numerous detections of water and other molecules in disks with the Spitzer-IRS (Salyk et al. 2008; Carr Najita 2008) have provided one of the first opportunities to study the chemistry of terrestrial planet-forming regions in protoplanetary disks. I will present results from the Spitzer program 'Water and organics in disks' (PI: J. Carr), and discuss possible implications of these results in the context of disk models. These include strong differences in detection frequencies between low- and mid-mass stars, and between classical and transitional disks, a dependence in detection frequency on grain settling, and possible evidence for freeze-out at small radii. I will also discuss ongoing complementary observations at ground-based facilities, and with the Herschel Space Observatory, including the Open Time program `Cool Herschel/Hot Spitzer: The distribution of water in protoplanetary disks' (PI: K. Pontoppidan).

Robert McMahon (University of Wisconsin)

Organic Reactive Intermediates and the Chemistry of Interstellar Space

Our recent research efforts focus on elucidating the structure, photochemistry, and spectroscopy of organic species that are postulated to play a role in the chemistry of the interstellar medium. Interstellar clouds contain a remarkable diversity of organic functionality, including reactive intermediates such as radicals and carbenes. We have drawn on our knowledge of mechanistic and structural organic chemistry to identify chemically-significant targets for detection by radio astronomy. These targets represent key species whose detection will provide important insight concerning chemical processes in space.

Through collaborations with molecular spectroscopists, laboratory data that are required for astronomical searches have been obtained.1-4 An investigation concerning the structure and rotational spectroscopy of the phenyl radical (2) and o-benzyne (3) will be described. Phenyl (2) is a crucial intermediate in combustion and soot formation, and may play a role in the chemistry of space. Astronomical observations to detect o-benzyne (3) in protoplanetary nebula CRL 618 provide important constraints for chemical models of astronomical environments.5

The wealth of new observational data from ALMA will provide the opportunity to explore the complex chemistry of astronomical environments. We will coordinate our own research activities to assist in making chemical sense of the data obtained by ALMA.

(1) McMahon, R. J.; Halter, R. J.; Fimmen, R. L.; Wilson, R. J.; Peebles, S. A.; Kuczkowski, R. L.; Stanton, J. F., J. Am. Chem. Soc. 2000, 122, 939-949. (2) Halter, R. J.; Fimmen, R. L.; McMahon, R. J.; Peebles, S. A.; Kuczkowski, R. L.; Stanton, J. F., J. Am. Chem. Soc. 2001, 123, 12353 - 12363. (3) McMahon, R. J.; McCarthy, M. C.; Gottlieb, C. A.; Dudek, J. B.; Stanton, J. F.; Thaddeus, P., Astrophys. J. 2003, 590, L61-L64. (4) Lovas, F. J.; McMahon, R. J.; Grabow, J.-U.; Schnell, M.; Mack, J.; Scott, L. T.; Kuczkowski, R. L., J. Am. Chem. Soc. 2005, 127, 4345-4349. (5) Widicus Weaver, S. L.; Remijan, A. J.; McMahon, R. J.; McCall, B. J., Astrophys. J. 2007, 671, L153-L156.

Jay Lockman (NRAO - GB)

Glen Langston (NRAO - GB)

Spectroscopy with the Green Bank Telescope -- The Next Generation

The 100 meter Green Bank Telescope (GBT) is entering a new era with its next generation of receivers and detectors for astronomical spectroscopy. The developments take the form of extended frequency coverage into the 3mm band, multi-pixel focal plane arrays, phased-array feeds, and a new spectrometer. Prompted by recent improvements in the GBT surface and pointing, a two-pixel receiver is now under construction to provide spectroscopic capabilities at 10" angular resolution over 68-92 GHz, a part of the spectrum not now covered by any major facility. It should be available for the 2011-2012 winter observing season. The first GBT spectroscopic focal plane array, a seven-beam high sensitivity receiver for 18-26 GHz, was recently completed, along with a data reduction pipeline. The first results from this instrument will be presented. Development is under way on a focal plane array for the 84-116 GHz portion of the 3mm band. In addition, a prototype phased array feed receiver for spectroscopy at 1.4 GHz is being built. It will provide 7 closely spaced beams for mapping the 21cm line. A new detector based on CASPER technology is also under development. These efforts will make the GBT quite complementary to ALMA and a necessary component of many research programs.

David Wilner (Harvard-Smithsonian CfA)

ALMA Early Science and Beyond

ALMA will be transformative for studies of cool components of the Galaxy, in particular the molecular gas and dust in the immediate vicinity of young or evolved stars where arcsecond or higher resolution will be especially valuable to probe structure, dynamics, and chemistry.

At the start of Early Science scheduled for 2011, the subset of available ALMA antennas already will provide spectral line and continuum sensitivity and imaging capabilities that exceed any of the existing millimeter arrays. Using examples from star-forming regions and circumstellar disks, I will illustrate how a prospective ALMA user can realize the fantastic potential of this new facility in the Early Science stage and beyond.

Monday, January 17, 2011

Darek Lis (Caltech)

Isotopic Ratios in the Interstellar Medium and Solar System Materials  (Invited talk)

Isotopic ratios are an important tool in the study of the chemical evolution of the Galaxy and the origin of interstellar and solar system materials. Radio and submillimeter wavelengths, which are not affected by dust extinction, play a key role in the determination of isotopic ratios throughout the Galaxy. I review the current status of the field and future prospects in the ALMA era, focusing on recent measurements of hydrogen and nitrogen isotopes. These elements display the largest isotopic variations in the solar system, typically explained by mixing of the various protosolar and pre-solar reservoirs. They also provide key constraints for astrochemical fractionation models.

Rachel Friesen (NRAO)

James Di Francesco (NRC-HIA)
Phil Myers (CfA)
Arnaud Belloche (MPIfR)
Yancy Shirley (U. Arizona)
Tyler Bourke (CfA)

Depletion and Deuterium Fractionation in a Clustered Star-Forming Core

Systematic observations of multiple molecular species have greatly enhanced our understanding of the density, temperature, velocity and abundance profiles of starless and protostellar cores in isolation, and are necessary to follow the evolution of dense gas to star. With the goal of characterizing the physical conditions of dense gas in cores forming multiple stars, we present the results of systematic mapping of expected dense gas tracers (including NH3, N2H+, N2D+ and H2D+) towards a dense, fragmented core in the Ophiuchus molecular cloud. We find strong evidence that NH3 and N2H+ do not trace the coldest and densest locations of the core. In particular, we see significant offsets between objects identified in continuum emission and in NH3 and N2H+, in contrast with typical good correspondence found in isolated regions. Moreover, we find relatively low fractional NH3 and N2H+ abundance at the positions of continuum objects, and a general trend of decreasing fractional abundance of both species with increasing H2 column density. Distributions across Oph B2 of the deuterated species N2D+ and H2D+ follow more closely the continuum emission, but we find no abundance trend with column density, density, or gas temperature. An observed anticorrelation in deuterium fractionation with proximity to embedded protostars, however, suggests that even low-mass protostars can significantly impact the chemistry of larger-scale, cluster-forming cores.

Joseph McMullin (NRAO)

Claire J. Chandler (NRAO - SOC)
Miller Goss (NRAO - SOC)
Steven Myers (NRAO - SOC)
Goran Sandell (SOFIA)

Exploring Shock Chemistry in Star Forming Regions with the EVLA

Signatures of outflow activity in star forming regions were recognized over 40 years ago and, with the discovery of the widespread occurrence of bipolar CO outflows in the 1980s, understood to be a fundamental aspect of early stellar evolution. The outflows deposit large amounts of energy throughout the region, shocking ambient gas and altering the chemical composition of surrounding material through the addition of energy and new material (grain sputtering/vaporization). Several key molecular species have been distinguished in illustrating localized abundance enhancements associated with outflow activity and can be used to delineate the impact of the outflows on the surrounding environment.

We report on an exploratory project with the EVLA (Expanded Very Large Array) which details the environment of the NGC 1333 IRAS 4 star forming region from the perspective of several shock tracer molecules.

Sheng-Yuan Liu (ASIAA)

Vivien H.-R. Chen (National Tsing Hua University, Taiwan)
Yu-Nung Su (ASIAA, Taiwan)
Qizhou Zhang (CfA)

Deuterium Fractionation of Massive Star Forming Clumps in Infrared Dark Clouds

In the early evolutionary stages of star formation process, sequential depletion of molecular species on grain mantles nurtures a peculiar low-temperature chemistry due to the removal of important gas-phase reactants. One example is the removal of the gas-phase CO, which promotes ion-molecular reactions and consequently induces a sharp increase in the abundance of deuterated molecules in dense cores. This chemical signature has profound implications as being an indicator of the thermal history and evolutionary stages of star forming cores. In the case of low-mass star-formation, studies have shown that the deuterium fractionation of N2H+, N(N2D+)/N(N2H+), exhibits an increasing trend with dynamical age in the prestellar phase but a decreasing trend in the protostellar phase, just as is anticipated by chemical models considering the variation of kinetic temperature as well as the gas-phase CO abundances in these objects. There is so far less evidence of a consistent behavior of this deuterium fractionation in the case of high-mass protostellar candidates. In this presentation, we show our recent investigation of deuterium fractionation over a sample of massive star-forming clumps in infrared dark clouds, and demonstrate the moderate trend in their N(N2D+)/N(N2H+) with evolutionary stage, a behavior resembling what previously found in low-mass protostellar cores.

Nuria Marcelino (NRAO-CV)

B. Tercero and J. Cernicharo (Centro de Astrobiologia (CSIC-INTA), Madrid, Spain)
E. Roueff (Observatoire de Paris-Meudon, Paris, France)
A. Palau (Institut de Ciencies de l'Espai (CSIC-IEEC), Barcelona, Spain)
J.R. Goicoechea (Centro de Astrobiologia (CSIC-INTA), Madrid, Spain)
E. Bergin and the HEXOS team (Dept. of Astronomy, Univ. of Michigan, USA)

Warm Deuteration of Hydrogen Cyanide in Orion

Deuterium fractionation has been observed both in cold molecular clouds and in star forming regions. In the latter it should be a remnant from the earlier cold prestellar phase where, after being frozen onto dust grains, deuterated species are released during the switch-on of the hot and young protostar. However this mechanism does not explain the large deuteration ratios observed at regions with moderate temperatures such as the Orion Bar and the molecular Ridge.

Using HIFI data from the Guaranteed Time Key Program <#133#>Herschel observations of EXtra-Ordinary Sources<#133#> (HEXOS), we have detected high-J transitions arising from DCN, up to J=17--16, toward Orion KL. On the other hand, DNC is not detected in those HIFI bands already observed in the survey. Furthermore, the DCN J=2--1, J=2-1, 2'x2' maps observed with the IRAM 30m telescope reveal that DCN emission is widely extended along the molecular filament. Strong emission from Orion-S is also detected. These maps show two main emission peaks: one toward the position of the Compact Ridge, and a second one at the Extended Ridge. This strongly suggests, not only the extended distribution of this species, but also both the moderate and warm conditions under DCN seems to be produced (Extended and Compact Ridge, Hot Core and Orion-S). On the other hand, DNC J=2--1 emission is less extended than DCN and it does not show an emission peak at the KL position but only toward the Extended Ridge.

In our analysis we have combined the HIFI data with that of the Orion surveys performed at the 30m telescope, thus including a wide range of excitation conditions. In order to reproduce the observed profiles we have used the LVG approximation and a source model with a three layer stratification for the Compact Ridge, Plateau and Hot Core components. With this source structure, we were able to reproduce the mid to high-J transitions observed with HIFI. Results show indeed a higher deuteration of HCN in comparison with HNC. While the obtained DCN/HCN ratio is similar to that of DNC/HNC in the Extended Ridge (Tkin = 60 K), it is about one order of magnitude higher than that of DNC/HNC, for the Compact Ridge and the Hot Core components (Tkin = 100-300 K), suggesting different deuteration pathways for these two isomers.

This study demonstrates that observations of transitions covering a wide range of excitation conditions are mandatory in order to better constrain the physical properties in such a complex region as Orion. This was possible thanks to the high-J transitions accesible to Herschel-HIFI. In the future ALMA will provide observations in such a wide range of frequencies using the same instrument, together with high resolution maps allowing the identification of the main deuteration source.

Liz Humphreys (ESO)

Ciriaco Goddi (ESO)
Lynn Matthews (MIT)
Lincoln Greenhill (Harvard-Smithsonian CfA)
Claire Chandler (NRAO)

The KaLYPSO Project: Decoding Orion Source I

I will give an overview of the work of the KaLYPSO Team in understanding the process of high-mass star formation through study of radio Orion Source I. Spectroscopic results from the VLBA (19 epochs), the VLA and the GBT will be presented and discussed in conjunction with both radiative transfer and dynamical modelling. Prospects for deepening understanding of this source, and of the high-mass star formation process in general, in the ALMA era will be discussed.

Cécile Favre (Aarhus University (IFA))

Despois Didier (Laboratoire d'Astrophysique de Bordeaux (LAB))
Brouillet Nathalie (LAB)
Baudry Alain (LAB)
Wootten Al (NRAO)
Combes Françoise (LERMA)

HCOOCH3 as a probe of temperature and structure of Orion-KL

The Orion Kleinmann-Low nebula is the closest (414 pc) and the most studied massive star formation region. Several components (Hot Core, Plateau, Compact Ridge and Extended Ridge) are associated with Orion-KL. These have different chemical and physical properties: distinct spectral signatures and kinetic temperatures, different spatial distributions in complex molecules [1]. Whereas its proximity allows studies on a scale of a few hundred AU (or down to <50 AU in molecular H2 emission), spectral confusion makes it difficult to identify molecules with low abundances. We used high spectral and spatial resolution millimetre observations (from 7" to 2" and from 2.3 km/s to 0.4 km/s, respectively) from the Plateau de Bure Interferometer in order to reduce the spectral confusion.

Using the high angular resolution of 1.8"x0.8" we have focused our study on an important oxygenated molecule, methyl formate HCOOCH3, to characterize the physical conditions, temperature and density of the various molecular components. We identify 28 methyl formate emission peaks of which the two strongest ones are in the Compact Ridge and in the South West of the Hot Core [2].

Our observations show that 1) the Compact Ridge region seems to be heated by external mechanisms (e.g. shocks), 2) the LSR velocity of the gas is between 7.5 and 8.0 km/s depending on the positions, 3) a second velocity component at 9-10 km/s is identified along a North-South structure including the Compact Ridge and the BN object, 4) a very clear association is found between our methyl formate maps and the 2.12 μm excited H2 maps [3]. This tends to confirm a scenario of HCOOCH3 production involving the release of molecules from ice mantles, either methyl formate itself or a precursor, for example CH3OH.

1. Guélin, M., Brouillet, N., Cernicharo, J., Combes, F. Wootten, A. 2008, Astrophysics and Space Science, 313, 45-51
2. Favre, C., Despois, D., Brouillet, N., Baudry, A., Combes, F., Guélin, M., Wootten, A.
Wlodarczak, G. 2010, Astronomy Astrophysics, submitted
3. Nissen, H. D., Gustafsson, M., Lemaire, J. L., Clénet, Y., Rouan, D.
Field, D. 2007, Astronomy Astrophysics, 466, 949

 Page last updated 1 February 2011 by GHMS