Detection of neutral carbon in the M 31 dark cloud D 478

F. P. Israel, R. P.J. Tilanus, F. Baas

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

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 languageEnglish (US)
Pages (from-to)398-404
Number of pages7
JournalAstronomy and astrophysics
Volume339
Issue number2
StatePublished - Nov 10 1998
Externally publishedYes

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

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