Extracting HI Astrophysics from Interferometric Intensity Mapping
  We present a new halo model of neutral hydrogen (HI) calibrated to galaxy
formation simulations at redshifts $z\sim0.1$ and $z\sim1.0$ that we employ to
investigate the constraining power of interferometric HI intensity mapping on
HI astrophysics. We demonstrate that constraints on the small-scale HI power
spectrum can break the degeneracy between the HI density $\Omega_{\rm HI}$ and
the HI bias $b_{\rm HI}$. For $z\sim0.1$, we forecast that an accurate
measurement of $\Omega_{\rm HI}$ up to 6% level precision and the large-scale
HI bias $b_{\rm HI}^0$ up to 1% level precision can be achieved using Square
Kilometre Array (SKA) pathfinder data from MeerKAT and Australian SKA
Pathfinder (ASKAP). We also propose a new description of the HI shot noise in
the halo model framework in which a scatter of the relation between the HI mass
of galaxies and their host halo mass is taken into account. Furthermore, given
the number density of HI galaxies above a certain HI mass threshold, future
surveys will also be able to constrain the HI mass function using only the HI
shot noise. This will lead to constraints at the 10% level using the standard
Schechter function. This technique will potentially provide a new way of
measuring the HI Mass Function, independent from existing methods. We predict
that the SKA will be able to further improve the low-redshift constraints by a
factor of 3, as well as pioneering measurements of HI astrophysics at higher
redshifts.
