Reionization scenarios and the temperature of the intergalactic medium

We examine the temperature structure of the intergalactic medium ( IGM) due to the passage of individual ionization fronts using a radiative transfer ( RT) code coupled to a particle- mesh N- body code. Multiple simulations were performed with different spectra of ionizing radiation: a power law (alpha nu(-0.5)), miniquasar, starburst, and a time- varying spectrum that evolves from a starburst spectrum to a power law. The RT is sufficiently resolved in time and space to correctly model both the ionization state and the temperature across the ionization front. We find that the post- ionization temperature of the reionized IGM is sensitive to the spectrum of the source of ionizing radiation, which may be used to place strong constraints on the nature of the sources of reionization. RT effects also produce large fluctuations in the He II to HI number density ratio eta. The spread in values is smaller than measured, except for the time- varying spectrum. For this case, the spread evolves as the spectral nature of the ionizing background changes. Large values for eta are found in partially ionized He II as the power- law spectrum begins to dominate the starburst, suggesting that the large eta values measured may be indicating the onset of the He II reionization epoch.