The $HI$- and $H_{2}$-to-stellar mass correlations of late- and early-type galaxies and their consistency with the observational mass functions

A. R. Calette, Vladimir Avila-Reese, Aldo Rodríguez-Puebla, Héctor Hernández-Toledo, Emmanouil Papastergis

Published 2018-03-20Version 1

We compile from the literature many local galaxy samples (mostly from follow-up radio observations of optically-selected samples) with available information on stellar mass, morphology, and HI and/or $H_{2}$ gas content. After homogenizing the data and handling adequately the reported upper limits in the case of non gas detections, we determine the $HI$- and $H_{2}$-to-stellar mass correlations (mean and standard deviation) of galaxies separated into two main populations, late- and early-type galaxies (LTGs and ETGs, respectively). The correlations are described by either a single or double power law, but at the low-mass side, some hints of flattening are found, with transition masses close to the one that separates normal and dwarf galaxies, $M_{\ast}\approx 1-2\times 10^{9}M_{\odot}$. LTGs are significantly gas richer than ETGs, specially at the highest masses. The respective $H_{2}$-to-$HI$ mass ratios as a function of $M_{\ast}$ are presented. Further, we attempt to constrain the corresponding full distributions of the $HI$- and $H_{2}$-to-stellar mass ratios as a function of $M_{\ast}$ for both LTGs and ETGs. A Schechter function for the former and a (broken) Schechter + uniform function for the latter, with the function parameters depending on $M_{\ast}$, provide reasonable descriptions of the data (detections and non detections). By using the observed galaxy stellar mass function and volume-complete fractions of LTGs/ETGs as a function of $M_{\ast}$, these empirical distributions are mapped into $HI$ and $H_{2}$ mass functions. The obtained total $HI$ and $H_{2}$ mass functions are in reasonable agreement with those inferred from observations. The empirical gas-to-stellar mass correlations and distributions for local LTGs and ETGs presented here can be used to constrain models and simulations of galaxy evolution.