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Low density molecular gas in the galaxy

Usuda, K. S.; Hasegawa, T.; Handa, T.; Morino, J. I.; Sawada, T.; Sakamoto, S.; Oka, T.; Seta, M.; Sorai, K.; Hayashi, M.; Booth, R.; Nyman, L. A.; Bronfman, L.; May, J.; Luna, A.; Shaver, P. and White, G. J. (1999). Low density molecular gas in the galaxy. In: The Physics and Chemistry of the Interstellar Medium, 22-25 September 1998, Zermatt, p. 96.

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Abstract

The distributions and physical conditions in molecular gas in the interstellar medium have been investigated in both the Galaxy and towards external galaxies. For example, Galactic plane surveys in the CO J =1-0 line with the Columbia 1.2-m telescope and with the Five College Radio Astronomy Observatory (FCRAO) 14-m telescopes have been able to trace spiral arms more clearly than HI surveys have been able to reveal, and indicate that most of molecular mass is contained in Giant Molecular Clouds (GMCs). Extensive maps of the whole Milky Way showed two prominent features, the 4-kpc molecular ring and the Galactic center. The physical conditions in the Galaxy have been studied by comparing the intensity of CO J =1-0 line with those of other lines, e.g., 13CO J =1-0, higher J transitions of CO, and dense gas tracers such as HCO+, CS, and HCN.

Previous studies were however strongly biased towards regions where CO emission was known to be intense. The radial distribution of molecular hydrogen shows that most of the H2 gas which is indirectly traced by observations of its associated CO emission, originates from the inner Galaxy (Dame 1993). Extending outwards from a galacto-centric distance of ~7 kpc, the H2 mass surface density decreases dramatically, and HI dominates over H2 in the outer Galaxy. What are physical conditions of molecular gas where the CO emission is relatively weak, and can we really trace all of the molecular gas through obervations of CO? These kinds of problems have not been solved yet, but are addressed in our study.

Item Type: Conference Item
Copyright Holders: 1999 Not known
Extra Information: The Physics and Chemistry of the Interstellar Medium, Proceedings of the 3rd Cologne-Zermatt Symposium,
held in Zermatt, September 22-25, 1998,
Eds.: V. Ossenkopf, J. Stutzki, and G. Winnewisser,
GCA-Verlag Herdecke,
ISBN 3-928973-95-9
pp.96-99
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 33301
Depositing User: Glenn White
Date Deposited: 25 Apr 2012 09:37
Last Modified: 26 Apr 2012 16:07
URI: http://oro.open.ac.uk/id/eprint/33301
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