HI-selected Galaxies as a probe of Quasar Absorption Systems
  We investigate the properties of HI-rich galaxies detected in blind radio
surveys within the hierarchical structure formation scenario using a
semi-analytic model of galaxy formation. By drawing a detailed comparison
between the properties of HI-selected galaxies and HI absorption systems, we
argue a link between the local galaxy population and quasar absorption systems,
particularly for Damped Ly-alpha absorption (DLA) systems and sub-DLA systems.
First, we evaluate how many HI-selected galaxies exhibit HI column densities as
high as those of DLA systems. We find that HI-selected galaxies with HI masses
M(HI) > 10^8 solar masses have gaseous disks that produce HI column densities
comparable to those of DLA systems. We conclude that DLA galaxies where the HI
column densities are as high as those of DLA systems, contribute significantly
to the population of HI-selected galaxies at M(HI) > 10^8 solar masses. Second,
we find that star formation rates (SFRs) correlate tightly with HI masses
rather than B- (and J-) band luminosities.
  In the low-mass range M(HI) < 10^8 solar masses, sub-DLA galaxies replace DLA
galaxies as the dominant population. The number fraction of sub-DLA galaxies
relative to galaxies reaches 40%-60% at HI masses 10^8 solar masses and 30%-80%
at 10^7 solar masses. The HI-selected galaxies at 10^7 solar masses are a
strong probe of sub-DLA systems that place stringent constraints on galaxy
formation and evolution.
