SIMBAD references

We revisit the mass ratio η_galaxy between molecular hydrogen (H₂) and atomic hydrogen (Hi) in different galaxies from a phenomenological and theoretical viewpoint. First, the local H₂ mass function (MF) is estimated from the local CO luminosity function (LF) of the FCRAO Extragalactic CO Survey, adopting a variable CO-to-H₂ conversion fitted to nearby observations. This implies an average H₂ density and in the local Universe. Secondly, we investigate the correlations between η_galaxy and global galaxy properties in a sample of 245 local galaxies. Based on these correlations we introduce four phenomenological models for η_galaxy, which we apply to estimate H₂ masses for each Hi galaxy in the HIPASS catalogue. The resulting H₂ MFs (one for each model for η_galaxy) are compared to the reference H₂ MF derived from the CO LF, thus allowing us to determine the Bayesian evidence of each model and to identify a clear best model, in which, for spiral galaxies, η_galaxy negatively correlates with both galaxy Hubble type and total gas mass. Thirdly, we derive a theoretical model for η_galaxy for regular galaxies based on an expression for their axially symmetric pressure profile dictating the degree of molecularization. This model is quantitatively similar to the best phenomenological one at redshift z = 0, and hence represents a consistent generalization while providing a physical explanation for the dependence of η_galaxy on global galaxy properties. Applying the best phenomenological model for η_galaxy to the HIPASS sample, we derive the first integral cold gas MF (Hi + H₂+ helium) of the local universe.