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R.I. Diaz-Miller, R.J. Allen (Space Telescope Science Institute), J.-C. Cuillandre (Canada-France-Hawaii Telescope), J. Lequeux (Observatoire de Paris)
Recent observations carried by Cuillandre et al. (2000) show the presence of dust and blue main sequence stars in the outerskirts of M31. This area extends from 23 to 33 Kpc from the center and is associated with extended HI features. Although molecular gas has not been directly identified in this region, the presence of dust implies the presence of the molecular gas, in agreement with the observation of young stars. The good correspondence between the observed HI and the number of identified B stars, on the other hand, indicates that photodissociation may possibly be the source of the neutral gas in this area. We model the distribution of photodissociated gas that is produced by the observed stellar population for a range of plausible values of the volume density of the underlying molecular gas. Since there is no information on the FUV flux in this region, theoretical atmosphere models are used to infer the photodissociation rates.
The author(s) of this abstract have provided an email address for comments about the abstract: rmiller@stsci.edu