Probing Cosmological Reionization through Radio-interferometric
  Observations of Neutral Hydrogen
  The epoch of reionization is one of the least known chapters in the
evolutionary history of the Universe. This thesis investigates two major
approaches to unveil the reionization history of the Universe using HI 21-cm
maps.The most discussed approach has been to study the global statistical
properties of the reionization HI 21-cm. We develop the formalism to calculate
the Multi-frequency Angular Power Spectrum (MAPS) and quantify the statistics
of the HI signal as a joint function of the angular multipole l and frequency
separation \Delta\nu. We adopt a simple model for the HI distribution which
incorporates patchy reionization and use it to study the signatures of ionized
bubbles on MAPS. We also study the implications of the foreground subtraction.
A major part of the thesis investigates the possibility of detecting ionized
bubbles around individual sources in 21-cm maps. We present a visibility based
matched filter technique to optimally combine the signal from an ionized bubble
and minimize the noise and foreground contributions. The formalism makes
definite predictions on the ability to detect an ionized bubble or conclusively
rule out its presence within a radio map. Results are presented for the GMRT
and the MWA. Using simulated HI maps we analyzed the impact of HI fluctuations
outside the bubble on its detectability. Various other issues such as (i)
bubble size determination (ii) blind search for bubbles, (iii) optimum redshift
for bubble detection are also discussed.
