Infoscience

Conference paper

Neutral hydrogen in the local universe

We revisit the composition of neutral hydrogen, i.e. atomic (HI) and molecular (H2), in the local Universe, with focus on the H2-to-HI mass ratio R in various galaxies and the H2-mass function (MF). First, we derive the H2-MF from the CO-luminosity function (LF) of the FCRAO Extragalactic CO Survey, using a variable CO-to-H2 conversion fitted to nearby observations. This implies a universal H2 density Omega(H2)=(6.9±2.7)*10^-5/h and Omega(H2)/Omega(HI)=0.26±0.11, which could, however, suffer from incompleteness of the CO-sample. Therefore, a second approach derives the H2-MF from a HI-sample with well described completeness (HIPASS). This premisses an estimation of R, for which we introduce a set of phenomenological models based on a sample of 245 galaxies drawn from the literature. Our best model in terms of statistical scatter describes R as a function of galaxy type and cold gas mass. This model leads to an H2-MF that matches the one derived from the CO-LF, thus supporting that model and settling completeness uncertainties.

Related material

Contacts