Simulating the epoch of Helium reionization in photon conserving semi numerical code SCRIPT

Helium reionization refers to the cosmic epoch when the second electron of helium (HeII) gets ionized, predominantly due to quasars and ends at z~3. The impact of helium reionization on the thermal and ionization state of the IGM has important implications for using the Lyman alpha forest for precision cosmology at these redshifts. In this talk I will present efficient semi numerical simulations to model the thermal and ionization state of the IGM during helium reionization. For this purpose we modified SCRIPT, which was originally developed for modelling hydrogen reionization. The resolution convergence of SCRIPT allows for running coarse grid simulations, leading to an improved computational efficiency. We make appropriate modifications to SCRIPT for modeling inhomogenous helium reionization and the corresponding thermal history of the IGM is modelled via a subgrid prescription. Our model has three main free parameters i.e. the global clumping factor (C), the temperature increase due to photoheating (𝑇_𝑟𝑒) and the quasar spectral energy distribution (SED) index, (𝛼_𝑈𝑉). Our fiducial model reproduces the average empirical measurements of the ionization and thermal history of the IGM during this epoch. The efficiency of our semi numerical model shows promising prospects for parameter estimation during this epoch in future, using measurements of the HeII Lyman alpha forest. I will also briefly touch upon how we intend to model the Lyman alpha forest measurements in our coarse grid simulation box.