Michael G. Burton1, Michael C. B. Ashley1, Catherine Braiding1, John W. V. Storey1, Craig Kulesa2, David J. Hollenbach3, Mark Wolfire4, Christian Glück5, and Gavin Rowell6
http://m.iopscience.iop.org/0004-637X/782/2/72/refs/37/doi
m.burton@unsw.edu.au
m.burton@unsw.edu.au
1 School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
2 Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
3 Carl Sagan Center, SETI Institute, 189 Bernado Avenue, Mountain View, CA 94043-5203, USA
4 Astronomy Department, University of Maryland, College Park, MD 20742, USA
5 KOSMA, I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
6 School of Chemistry and Physics, University of Adelaide, Adelaide, SA 5005, Australia
2 Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
3 Carl Sagan Center, SETI Institute, 189 Bernado Avenue, Mountain View, CA 94043-5203, USA
4 Astronomy Department, University of Maryland, College Park, MD 20742, USA
5 KOSMA, I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
6 School of Chemistry and Physics, University of Adelaide, Adelaide, SA 5005, Australia
Received 26 September 2013, accepted for publication 23 December 2013. Published 29 January 2014.
© 2014. The American Astronomical Society. All rights reserved.
Abstract
We present spectral line images of [C I] 809 GHz, CO J = 1-0 115 GHz and H I 1.4 GHz line emission, and calculate the corresponding C, CO and H column densities, for a sinuous, quiescent giant molecular cloud about 5 kpc distant along the l = 328° sightline (hereafter G328) in our Galaxy. The [C I] data comes from the High Elevation Antarctic Terahertz telescope, a new facility on the summit of the Antarctic plateau where the precipitable water vapor falls to the lowest values found on the surface of the Earth. The CO and H I data sets come from the Mopra and Parkes/ATCA telescopes, respectively. We identify a filamentary molecular cloud, ~75 × 5 pc long with mass ~4 × 104 M ☉ and a narrow velocity emission range of just 4 km s–1. The morphology and kinematics of this filament are similar in CO, [C I], and H I, though in the latter appears as self-absorption. We calculate line fluxes and column densities for the three emitting species, which are broadly consistent with a photodissociation region model for a GMC exposed to the average interstellar radiation field. The [C/CO] abundance ratio averaged through the filament is found to be approximately unity. The G328 filament is constrained to be cold (T Dust < 20 K) by the lack of far-IR emission, to show no clear signs of star formation, and to only be mildly turbulent from the narrow line width. We suggest that it may represent a GMC shortly after formation, or perhaps still in the process of formation.
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