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For refcode 1995A&A...300L..13B:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1995A&A...300L..13B Letter to the Editor The relationship between star formation activity and molecular gas content in spiral galaxies A. Boselli, G. Gavassi, J. Lequeux, V. Buat, F. Casoli, J. Dickey, and J. Donas DEMlRM, Observatoire de Paris, 61 Avenue de l' Observatoire, F-75014 Paris, France Present address: Max-Planck-Institut fur Kernphysik, Postfach 103980, D-69 117 Heidelberg, Germany Osservatorio Astronomico di Brera, via Brera 28, I-20121 Milano, Italy Laboratoire d'Astronomie Spatiale, Traverse du Siphon, F-13376 Marseille Cedex 12, France Department of Astronomy, University of Minnesota, 16 Church Street S.E., Minneapolis, MN 55455, USA Received 18 April 1995 / Accepted 30 May 1995 Abstract: We use CO observations of spiral galaxies in the Coma/A1367 supercluster to study the relation between their H_2_ mass and their star formation rate. The galaxies form a complete optically-selected sample, which is dominated by luminous objects. Contrary to the results of several previous studies, we find for this sample a positive correlation between the molecular gas content as derived from the ^12^CO(1-0) line intensity using a standard conversion factor X and the star formation activity as traced by the H{alpha} equivalent width and by the far- infrared emission, all quantities being normalized to the H luminosity or to the disk area of the galaxy. No such correlation had been found previously for samples of closer galaxies which are dominated by lower- luminosity objects. However for Virgo cluster galaxies this correlation exists for the brightest objects and is only absent at lower luminosities. Rather than indicating a genuine lack of relation between molecular gas and star formation, the observations may indicate that the use of a standard CO line intensity/H_2_ mass conversion factor X is meaningful only in massive galaxies such as the Milky Way. In low-mass galaxies the higher far-UV radiation field and the lower dust-to-gas ratio increase the amount of photodissociation and raise the numerical value of the conversion factor. Consequently, the amount of molecular hydrogen is underestimated for these galaxies if the conventional value of X is used. Presumably the value of X varies from galaxy to galaxy especially for the low-luminosity ones due to the strong non-linearity of the processes involved, introducing a large dispersion in the relation between star formation and CO emission. Key words: galaxies: general; ISM - star formation - radio lines: galaxies
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