Abstract-The Carbon Inventory in a Quiescent, Filamentary Molecular Cloud in G328

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

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
 

Michael G. Burton et al. 2014 ApJ 782 72. doi:10.1088/0004-637X/782/2/72
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.