EAS Publications Series
Volume 4, 2002Infrared and Submillimeter Space Astronomy: An International Colloquium to Honor the Memory of Guy Serra
|Page(s)||393 - 393|
|Published online||25 September 2002|
M. Giard, J.P. Bernard, A. Klotz and I. Ristorcelli (eds)
EAS Publications Series, 4 (2002) 393
The 12CO(1—0) to H2 conversion factor in normal late-type galaxies
Laboratoire d'Astrophysique de Marseille, BP. 8, traverse du Siphon, 13376 Marseille, France
2 DEMIRM, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
3 Universitá degli Studi di Milano-Bicocca, Dipartimento di Fisica, Piazza dell'Ateneo Nuovo 1, 20126 Milano, Italy
The molecular gas mass in nearby galaxies is generally estimated using 12CO(1-0) line intensities and assuming the X conversion factor between I(CO) and N(H2) measured in the solar neighborhood. It is however known that this X conversion factor is not universal since it changes with metallicity, cosmic ray density and UV radiation field. Far-IR data in the spectral range 100-1000 μm can be used to estimate the molecular gas content of late-type galaxies in an independent way of CO line measurements once a metallicity-dependent dust to gas ratio is assumed, allowing a direct estimate of X. This exercise is presented here for a large sample of galaxies with available multifrequency data using ISOPHOT and IRAS far-IR data. X spans from ~1020 mol cm-2 (K km s-1)-1 in giant spirals to ~1021 mol cm-2 (K km s-1)-1 in dwarf irregulars. The relationships between X and the UV radiation field (as traced by the Hα[NII]E.W.), the metallicity and the H band luminosity are analysed.
© EAS, EDP Sciences, 2002
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