* Astronomy

Title: The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the Gould Belt
Author: Rachel K. Friesen, Jaime E. Pineda (co-PIs), Erik Rosolowsky, Felipe Alves, Ana Chacón-Tanarro, Hope How-Huan Chen, Michael Chun-Yuan Chen, James Di Francesco, Jared Keown, Helen Kirk, Anna Punanova, Youngmin Seo, Yancy Shirley, Adam Ginsburg, Christine Hall, Stella S. R. Offner, Ayushi Singh, Héctor G. Arce, Paola Caselli, Alyssa A. Goodman, Peter G. Martin, Christopher Matzner, Philip C. Myers, Elena Redaelli

We present an overview of the first data release (DR1) and first-look science from the Green Bank Ammonia Survey (GAS). GAS is a Large Program at the Green Bank Telescope to map all Gould Belt star-forming regions with A_V \gtrsim 7 mag visible from the northern hemisphere in emission from NH3 and other key molecular tracers. This first release includes the data for four regions in Gould Belt clouds: B18 in Taurus, NGC 1333 in Perseus, L1688 in Ophiuchus, and Orion A North in Orion. We compare the NH3 emission to dust continuum emission from Herschel, and find that the two tracers correspond closely. NH3 is present in over 60% of lines-of-sight with A_V \gtrsim 7 mag in three of the four DR1 regions, in agreement with expectations from previous observations. The sole exception is B18, where NH3 is detected toward ~ 40% of lines-of-sight with A_V \gtrsim7 mag. Moreover, we find that the NH3 emission is generally extended beyond the typical 0.1 pc length scales of dense cores. We produce maps of the gas kinematics, temperature, and NH3 column densities through forward modeling of the hyperfine structure of the NH3 (1,1) and (2,2) lines. We show that the NH3 velocity dispersion, sigma_v, and gas kinetic temperature, T_K, vary systematically between the regions included in this release, with an increase in both the mean value and spread of sigma_v and T_K with increasing star formation activity. The data presented in this paper are publicly available.

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Title: First results from the Herschel Gould Belt Survey in Taurus
Authors: J. M. Kirk (1,2), D. Ward-Thompson (2), P. Palmeirim (3), Ph. Andre (3), M. J. Griffin (1), P. J. Hargrave (1), V. Konyves (3,9), J. P. Bernard (4,5), D. J. Nutter (1), B. Sibthorpe (6), J. Di Francesco (7,8), A. Abergel (9), D. Arzoumanian (3), M. Benedettini (10), S. Bontemps (11), D. Elia (10), M. Hennemann (3), T. Hill (3), A.Men'shchikov (3), F.Motte (3), Q. Nguyen-Luong (3,12), N. Peretto (3), S. Pezzuto (10), K. L. J. Rygl (10), S. I. Sadavoy (7,8), E. Schisano (10), N. Schneider (11,3), L. Testi (13), G. White (14,15) ((1) School of Physics and Astronomy, Cardiff University, UK, (2) Jeremiah Horrocks Institute, Preston, UK (3) Laboratoire AIM, SEA Saclay, France, (4) CNRS, Toulouse, France, (5) Universite de Toulouse, France, (6) UK ATC, Royal Observatory Edinburgh, UK, (7) NRCC-HIA, Victoria, Canada, (8) Department of Physics and Astronomy, University of Victoria, Canada, (9) Institut d'Astrophysique Spatiale, Orsay, France, (10) Istituto di Astrofisica e Planetologia Spaziali, Roma, Italy, (11) Universite de Bordeaux, Bordeaux, France, (12) Canadian Institute for Theoretical Astrophysics, University of Toronto, Canada, (13) ESO, Garching, Germany, (14) Rutherford Appleton Laboratory, UK, (15) The Open University, UK)

The whole of the Taurus region (a total area of 52 sq. deg.) has been observed by the Herschel SPIRE and PACS instruments at wavelengths of 70, 160, 250, 350 and 500 µm as part of the Herschel Gould Belt Survey. In this paper we present the first results from the part of the Taurus region that includes the Barnard 18 and L1536 clouds. A new source-finding routine, the Cardiff Source-finding AlgoRithm (CSAR), is introduced, which is loosely based on CLUMPFIND, but that also generates a structure tree, or dendrogram, which can be used to interpret hierarchical clump structure in a complex region. Sources were extracted from the data using the hierarchical version of CSAR and plotted on a mass-size diagram. We found a hierarchy of objects with sizes in the range 0.024-2.7 pc. Previous studies showed that gravitationally bound prestellar cores and unbound starless clumps appeared in different places on the mass-size diagram. However, it was unclear whether this was due to a lack of instrumental dynamic range or whether they were actually two distinct populations. The excellent sensitivity of Herschel shows that our sources fill the gap in the mass-size plane between starless and pre-stellar cores, and gives the first clear supporting observational evidence for the theory that unbound clumps and (gravitationally bound) prestellar cores are all part of the same population, and hence presumably part of the same evolutionary sequence (c.f. Simpson et al. 2011).

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Title: The Spitzer Survey of Interstellar Clouds in the Gould Belt. V. Ophiuchus North Observed with IRAC and MIPS
Authors: Jennifer Hatchell, Susan Terebey, Tracy Huard, Eric Mamajek, Lori Allen, Tyler Bourke, Michael Dunham, Robert Gutermuth, Paul Harvey, Jes Jorgensen, Bruno Merin, Albert Noriega-Crespo, Dawn Peterson

We present Spitzer IRAC (2.1 sq. deg.) and MIPS (6.5 sq. deg.) observations of star formation in the Ophiuchus North molecular clouds. This fragmentary cloud complex lies on the edge of the Sco-Cen OB association, several degrees to the north of the well-known rho Oph star-forming region, at an approximate distance of 130 pc. The Ophiuchus North clouds were mapped as part of the Spitzer Gould Belt project under the working name 'Scorpius'. In the regions mapped, selected to encompass all the cloud with visual extinction AV>3, eleven Young Stellar Object (YSO) candidates are identified, eight from IRAC/MIPS colour-based selection and three from 2MASS K/MIPS colours. Adding to one source previously identified in L43 (Chen et al. 2009), this increases the number of YSOcs identified in Oph N to twelve. During the selection process, four colour-based YSO candidates were rejected as probable AGB stars and one as a known galaxy. The sources span the full range of YSOc classifications from Class 0/1 to Class III, and starless cores are also present. Twelve high-extinction (AV>10) cores are identified with a total mass of approx. 100 solar masses. These results confirm that there is little ongoing star formation in this region (instantaneous star formation efficiency <0.34%) and that the bottleneck lies in the formation of dense cores. The influence of the nearby Upper Sco OB association, including the 09V star zeta Oph, is seen in dynamical interactions and raised dust temperatures but has not enhanced levels of star formation in Ophiuchus North.

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Herschel unravels the thread of star formation in the Gould Belt

An intricate network of filamentary structure, exposed in extraordinary detail by the Herschel Space Observatory, has provided new evidence for how stars form from the diffuse interstellar medium. These filaments, located in giant molecular clouds in the Gould Belt, all exhibit remarkably similar widths - about one third of a light year - but only the densest ones contain pre-stellar cores, the seeds of future stars. These data suggest star formation is a two-step process: first turbulence stirs up the gas, giving rise to a web-like structure, then gravity takes over and governs the further fragmentation of filaments into stars.
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