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
