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H2/CO Conversion Factor for M31 Molecular Clouds

Published online by Cambridge University Press:  12 April 2016

Yoahiaki Sofue ,
Mikio Takabayashi  and
Yasuhiro Murata
Yoahiaki Sofue
Affiliation:
Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181, Japan
Mikio Takabayashi
Affiliation:
Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181, Japan
Yasuhiro Murata
Affiliation:
Nobeyama Radio Observatory, Minamisaku, Nagano 384-13, Japan

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The conversion factor from the CO line intensity to column density of molecular hydrogen, X = NH2/ICO is one of the most important parameters in mm-wave study of galaxies and their molecular gas (e.g., Maloney 1990). Although the same value as that obtained for our Galactic clouds (e.g. Sanders et al. 1984; Bloemen et al. 1985) has been widely applied to galaxies, it is far from trivial that the conversion factor is universal among various types of galaxies. There have been few attempts to derive the value for galaxies, and the value is still controversial if it is applicable to other galaxies or not: Approximately the same value as that for the Galaxy has been derived for M33 (Wilson and Scoville 1990, 1992), while an order of magnitude larger value is obtained for the LMC and SMC (Cohen et al. 1988; Rubin et al. 1991).

In order to obtain the conversion factor in nearby galaxies, in which individual molecular clouds can be resolved, we are conducting CO-line mapping of M31. In this paper we report a preliminary results from mapping of a north-eastern spiral arm of M31 in the 12CO(J =1 − 0) line emission using the NMA.

Type
3. Astronomical Results and Prospects
Information
International Astronomical Union Colloquium , Volume 140: Astronomy with Millimeter and Submillimeter Wave Interferometry , 1994 , pp. 366 - 367
Copyright
Copyright © Astronomical Society of the Pacific 1994

References

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