Our Universe went through a prolonged period of changes during the epoch when the first collapsed structures formed (6 < z < 50). The radiation from the stars and accreting black holes in those structures partly escaped and changed the state of the Intergalactic Medium (IGM). The epoch of this global phase change – the IGM state was transformed from cold and neutral to warm and ionized – is called the Epoch of Reionization.

My work focuses on the photoheating of the IGM during this period. On one hand, I improve the cosmological radiative transfer code C2-RAY regarding the treatment of photoheating. On the other hand, I use the improved version of C2-RAY to study a photoheating-related observational feature exhibited by high redshift quasars.