H I-selected galaxies in hierarchical models of galaxy formation and evolution

Abstract

In this work, we study the basic statistical properties of H I-selected galaxies extracted from six different semi-analytic models, all run on the same cosmological N-body simulation. One model includes an explicit treatment for the partition of cold gas into atomic and molecular hydrogen. All models considered agree nicely with the measured H I mass function in the local Universe, with the measured scaling relations between H I and galaxy stellar mass, and with the predicted two-point correlation function for H I-rich galaxies. One exception is given by one model that predicts very little H I associated with galaxies in haloes above ∼10<SUP>12</SUP> M<SUB>☉</SUB>: we argue this is due to a too efficient radio-mode feedback for central galaxies, and to a combination of efficient stellar feedback and instantaneous stripping of hot gas for satellites. We demonstrate that treatment of satellite galaxies introduces large uncertainties at low H I masses. While models assuming non-instantaneous stripping of hot gas tend to form satellite galaxies with H I masses slightly smaller than those of centrals with the same stellar mass, instantaneous gas stripping does not translate necessarily in lower H I masses. In fact, the adopted stellar feedback and star formation affect the satellites too. We analyse the relation between H I content and spin of simulated haloes: low-spin haloes tend to host H I-poor galaxies, while high-spin haloes are populated by galaxies in a wide range of H I mass. In our simulations, this is due to a correlation between the initial gas disc size and the halo spin.