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 (~ν-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 HeII to HI number density ratio η. 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 η are found in partially ionized HeII as the power-law spectrum begins to dominate the starburst, suggesting that the large η values measured may be indicating the onset of the HeII reionization epoch.
|Journal||Monthly Notices of the Royal Astronomical Society|
|Publication status||Published - 1 Oct 2007|
- radiative transfer
- methods: N-body simulations
- methods: numerical
- diffuse radiation
- large-scale structure of Universe