HI as a Probe of the Large Scale Structure in the Post-Reionization
  Universe
  We model the distribution of neutral Hydrogen (HI hereafter) in the
post-reionization universe. This model uses gravity only N-Body simulations and
an ansatz to assign HI to dark matter haloes that is consistent with
observational constraints and theoretical models. We resolve the smallest
haloes that are likely to host HI in the simulations, care is also taken to
ensure that any errors due to the finite size of the simulation box are small.
We then compute the smoothed one point probability distribution function and
the power spectrum of fluctuations in HI. This is compared with other
predictions that have been made using different techniques. We highlight the
significantly high bias for the HI distribution at small scales. This aspect
has not been discussed before. We then discuss the prospects for detection with
the MWA, GMRT and the hypothetical MWA5000. The MWA5000 can detect visibility
correlations at large angular scales at all redshifts in the post-reionization
era. The GMRT can detect visibility correlations at lower redshifts,
specifically there is a strong case for a survey at z=1.3. We also discuss
prospects for direct detection of rare peaks in the HI distribution using the
GMRT. We show that direct detection should be possible with an integration time
that is comparable to, or even less than, the time required for a statistical
detection. Specifically, it is possible to make a statistical detection of the
HI distribution by measuring the visibility correlation, and, direct detection
of rare peaks in the HI distribution at z = 1.3 with the GMRT in less than 1000
hours of observations.
