MS. HAMSA PADMANABHAN

Recent observations of the ionized near-zones of quasars around redshift 6 have indicated an additional source of heating of the intergalactic medium, which has been claimed to be evidence for the beginning stages of helium reionization occurring at this redshift. In this talk, I describe how this effect may be studied with hydrodynamical simulations coupled to a radiative transfer code which we have developed. We find that the heating effect depends on the general equation of state of the IGM at that epoch, with steeper equations of state exhibiting less additional heating. This connects the heating due to helium reionization in the quasar near-zones, with the epoch of hydrogen reionization. The additional heating is also dependent on the initial neutral fraction of helium in the quasar vicinity, which points to constraints on single-step reionization scenarios. The heating effect may be effectively captured beyond the cosmic variance by using the curvature statistics, even if the sample size is half what is presently available. In the post-reionization universe, the 21-cm line of neutral hydrogen (HI) promises a powerful probe of the baryonic and dark matter distribution. I will describe how the combination of current observational and theoretical constraints on the neutral hydrogen density and the bias parameter lead to bounds on the power spectrum of HI intensity fluctuations over redshifts 0 to 4.