Two phase galaxy formation: The Gas Content of Normal Galaxies

We investigate the atomic (HI) and molecular (H2) Hydrogen content of normal galaxies by combining observational studies linking galaxy stellar and gas budgets to their host dark matter (DM) properties, with a physically grounded galaxy formation model. This enables us to analyse empirical relationships between the virial, stellar, and gaseous masses of galaxies and explore their physical origins. Utilising a semianalytic model (SAM) to study the evolution of baryonic material within evolving DM halos, we study the effects of baryonic infall, star formation and various feedback mechanisms on the properties of formed galaxies using the most up-to-date physical recipes. We find that in order to significantly improve agreement with observations of low-mass galaxies we must suppress the infall of baryonic material and exploit a two-phase interstellar medium (ISM), where the ratio of HI to H2 is determined by the galactic disk structure. Modifying the standard Schmidt-Kennicutt star formation law by correlating the star formation activity with the H2 gas mass allows us to simultaneously reproduce stellar, HI and H2 mass functions for normal galaxies.