Combined lensed estimator to probe the post reionization H I power
  spectrum
  In the post-reionization era, the baryons assembled into the protogalaxies
and eventually the present population of the galaxies evolved through merger
and evolution. In this work, we discuss a possible probe of the statistical
distribution and evolution of the H I density in the post reionization era. We
introduce an estimator of the H I power spectrum from the post reionization
universe by observing it through the strong gravitational lenses by the nearby
galaxy cluster. We also analytically calculate the uncertainties associated
with the estimates of the post-EoR power spectrum for the discussed estimator.
We access the efficacy of this estimator in the context of 19 galaxy clusters
for which the lensing potential has been estimated earlier by various authors.
We find that by combining the lensed power spectrum through eight of these
cluster lenses, it is possible to estimate the post-reionization H I power
spectrum at five-sigma significance for angular multipoles < 4000 for a uGMRT
observation of 16 MHz bandwidth from redshifts of 1.25, 1.5 with a total of 400
hours of observation. With the same setup, for a redshift of 3.0, we need 200
hours of total observation time. The estimator also suppresses the diffused
galactic foreground, though, the latter is still a dominant contributor to the
overall signal and hence need to be estimated and mitigated. We discuss the
merits and demerits of the estimator.
