HI-selected Galaxies in Hierarchical Models of Galaxy Formation and
  Evolution
  In this work, we study the basic statistical properties of HI-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 HI mass function in the local
Universe, with the measured scaling relations between HI and galaxy stellar
mass, and with the predicted 2-point correlation function for HI rich galaxies.
One exception is given by one model that predicts very little HI associated
with galaxies in haloes above 10^12 Msun: 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 HI masses. While models assuming non instantaneous
stripping of hot gas tend to form satellite galaxies with HI masses slightly
smaller than those of centrals with the same stellar mass, instantaneous gas
stripping does not translate necessarily in lower HI masses. In fact, the
adopted stellar feedback and star formation affect the satellites too. We
analyze the relation between HI content and spin of simulated haloes: low spin
haloes tend to host HI poor galaxies while high spin haloes are populated by
galaxies in a wide range of HI mass. In our simulations, this is due to a
correlation between the initial gas disk size and the halo spin.
