Radiative transfer through the intergalactic medium

We use a probabilistic method to compute the propagation of an ionization front corresponding to the reionization of the intergalactic medium in a Λ-cold dark matter (ΛCDM) cosmology, including both hydrogen and helium. The effects of radiative transfer substantially boost the temperature of the ionized gas over the case of uniform reionization. The resulting temperature–density relation of the ionized gas is both non-monotonic and multiple-valued, reflecting the non-local character of radiative transfer and suggesting that a single polytropic relation between local gas density and temperature is a poor description of the thermodynamical state of baryons in the post-reionization universe