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We study the ionization and thermal evolution of the intergalactic mediumduring the epoch of \heii reionization by means of radiation hydrodynamicalcosmological simulations. We post-process baryonic density fields from astandard optically-thin IGM simulation with a homogeneous galaxy-dominated UVbackground (UVB) which reionizes \hi and \hei at z=6.5 but does not have anycontribution to the ionization of \heii. Quasars with luminosities proportionalto the mass of the host halos are then introduced as point sources throughoutthe 100 Mpc simulation volume consistent with the Pei luminosity function. Weevolve the spatial distribution of the \heii ionizing radiation field using atime-implicit variable tensor Eddington factor radiative transfer scheme.Simultaneously, we also solve for the local ionization of \heii to \heii andthe associated photoheating of the gas. We find that the percolation of the\heiii regions is essentially complete by z=2.5. When comparing to aself-consistent optically thin simulation we find that in optically thickcalculation the gas temperature is higher by a factor of approximately 1.7 atthe mean gas density level. We use 300 random lines of sight to compute at$\bar{z} = 2.5 \pm 0.1$ a mean \heii \lya line transmission of $\bar{F} = 0.304\pm 0.002$. We compare the broadening width of the \hi and \heii \lya lines tothe results from the self-consistent optically thin simulation and find a shiftby approximately 1.25 km/s of the b-parameter distribution. Estimating therelative broadening width between the two forests shows that the \heii medianb-parameter is about 0.8 times the median \hi broadening width. This impliesthat the \heii absorbers are physically extended consistent with conclusionsfrom observed lines of sight.

Late Reheating of the IGM by Quasars: A Radiation Hydrodynamical Simulation of Helium II Reionization