The Halo Occupation Distribution of HI Galaxies
  We perform an analysis of the spatial clustering properties of HI selected
galaxies from the HI Parkes All Sky Survey (HIPASS) using the formalism of the
halo occupation distribution (HOD). The resulting parameter constraints show
that the fraction of satellite galaxies (i.e. galaxies which are not the
central member of their host dark matter halo) among HIPASS galaxies is <20%,
and that satellite galaxies are therefore less common in HIPASS than in
optically selected galaxy redshift surveys. Moreover the lack of fingers-of-god
in the redshift space correlation function of HIPASS galaxies may indicate that
the HI rich satellites which do exist are found in group mass rather than
cluster mass dark matter halos. We find a minimum halo mass for HIPASS galaxies
at the peak of the redshift distribution of M~10^11 solar masses, and show that
less than 10% of baryons in HIPASS galaxies are in the form of HI. Quantitative
constraints on HOD models from HIPASS galaxies are limited by uncertainties
introduced through the small survey volume. However our results imply that
future deeper surveys will allow the distribution of HI with environment to be
studied in detail via clustering of HI galaxies.
