Probing the thermal history during reionization using a semi-numerical photon-conserving code SCRIPT

The ionization and thermal state of the intergalactic medium (IGM) during the epoch of reionization has been of interest in recent times because of their close connection to the first stars. We present in this paper a semi-numerical code which computes the large-scale temperature and ionized hydrogen fields in a cosmologically representative volume accounting for the patchiness in these quantities arising from reionization. The code is an extension to a previously developed version for studying the growth of ionized regions, namely, Semi Numerical Code for ReionIzation with PhoTon Conservation (SCRIPT). The main additions in the present version are the inhomogeneous recombinations which are essential for temperature calculations. This extended version of SCRIPT also implements physical consequences of photoheating during reionization, e.g., radiative feedback. These enhancements allow us to predict observables which were not viable with the earlier version. These include the faint-end of the ultra-violet luminosity function of galaxies (which can get affected by the radiative feedback) and the temperature-density relation of the low-density IGM at $z\sim 6$. We study the effect of varying the free parameters and prescriptions of our model on a variety of observables. The conclusion of our analysis is that it should be possible to put constraints on the evolution of thermal and ionization state of the IGM using available observations accounting for all possible variations in the free parameters. A detailed exploration of the parameter space will be taken up in the future.