Abstract
Emission from the 3P1-3 P0 [CI] transition at 492 GHz has been detected towards the dark cloud D 478 in the Local Group galaxy M 31. Using literature detections of the lower 12CO and 13CO transitions, models for the gas distribution in D 478 are discussed. The observed CO and C line ratios can be explained by two-component models (high density cores and low-density envelopes); single-density models appear less likely. The models indicate kinetic temperatures of the order of Tk ≈ 10 K. The beam-averaged column density of neutral carbon is 0.3-0.8 times that of CO, whereas the total carbon to hydrogen ratio NC/NH is 5-3 × 10-4. The resulting CO to H2 conversion factor X is about half that of the Solar Neighbourhood. With temperatures of about 10 K and projected mass-densities of 5-10 M⊙ pc-2 there appears to be no need to invoke the presence of very cold and very massive clouds. Rather, D 478 appears to be comparable to Milky Way dark cloud complexes at the higher metallicity expected from its central location in M 31. In particular, several similarities between D 478 and the Galactic Taurus-Auriga dark cloud complex may be noted.
Original language | English (US) |
---|---|
Pages (from-to) | 398-404 |
Number of pages | 7 |
Journal | Astronomy and astrophysics |
Volume | 339 |
Issue number | 2 |
State | Published - Nov 10 1998 |
Externally published | Yes |
Keywords
- Galaxies: individual: M 31
- Galaxies: ISM
- ISM: individual objects: D 478
- ISM: molecules
- Radio lines: galaxies
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science