The halo mass function of late-type galaxies from HI kinematics
  We present an empirical method to measure the halo mass function (HMF) of
galaxies. We determine the relation between the \hi\ line-width from
single-dish observations and the dark matter halo mass ($M_{200}$) inferred
from rotation curve fits in the SPARC database, then we apply this relation to
galaxies from the \hi\ Parkes All Sky Survey (HIPASS) to derive the HMF. This
empirical HMF is well fit by a Schecther function, and matches that expected in
$\Lambda$CDM over the range $10^{10.5} < M_{200} <
10^{12}\;\mathrm{M}_{\odot}$. More massive halos must be poor in neutral gas to
maintain consistency with the power law predicted by $\Lambda$CDM. We detect no
discrepancy at low masses. The lowest halo mass probed by HIPASS, however, is
just greater than the mass scale where the Local Group missing satellite
problem sets in. The integrated mass density associated with the dark matter
halos of \hi-detected galaxies sums to $\Omega_{\rm m,gal} \approx 0.03$ over
the probed mass range.
