Simulating the Large-Scale Structure of HI Intensity Maps
  Intensity mapping of neutral hydrogen (HI) is a promising observational probe
of cosmology and large-scale structure. We present wide field simulations of HI
intensity maps based on N-body simulations of a $2.6\, {\rm Gpc / h}$ box with
$2048^3$ particles (particle mass $1.6 \times 10^{11}\, {\rm M_\odot / h}$).
Using a conditional mass function to populate the simulated dark matter density
field with halos below the mass resolution of the simulation ($10^{8}\, {\rm
M_\odot / h} < M_{\rm halo} < 10^{13}\, {\rm M_\odot / h}$), we assign HI to
those halos according to a phenomenological halo to HI mass relation. The
simulations span a redshift range of 0.35 < z < 0.9 in redshift bins of width
$\Delta z \approx 0.05$ and cover a quarter of the sky at an angular resolution
of about 7'. We use the simulated intensity maps to study the impact of
non-linear effects and redshift space distortions on the angular clustering of
HI. Focusing on the autocorrelations of the maps, we apply and compare several
estimators for the angular power spectrum and its covariance. We verify that
these estimators agree with analytic predictions on large scales and study the
validity of approximations based on Gaussian random fields, particularly in the
context of the covariance. We discuss how our results and the simulated maps
can be useful for planning and interpreting future HI intensity mapping
surveys.
