DR. PRAKASH GAIKWAD

The quasar driven He II reionization (2 <= z <= 4) is observationally more accessible than epoch of H I reionization (z <= 5.5). The observational uncertainty in quasar spectral energy distribution and non-equilibrium ionization effects are important in cosmological hydrodynamical simulations but are computationally expensive. We have incorporated these effects in our “Code for Ionization and Temperature Evolution” (CITE) that works in the post-processing step of state-of-the art GADGET simulation. We will discuss the effect of uncertainty in quasar spectral energy distribution and non-equilibrium He II ionization on thermal state of the IGM at 2 <= z <= 4. We also show the observational evidence for non-equilibrium ionization evolution and flatter quasar spectral energy distribution from quasar absorption spectra (H I and He II Lya forest).