Reionisation scenarios and the temperature of the IGM

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Abstract
We have explored reionisation of the universe using a radiative transfer (RT) code coupled to a particle-mesh (PM) N-body code. Multiple simulations were performed with different spectra of ionising radiation: a power law, 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 ionisation state and the temperature across the ionisation front. The temperature of the ionised intergalactic medium (IGM) is sensitive to the spectrum of the source of ionising radiation. The post-ionisation temperature is fairly insensitive to the redshift at which the hydrogen ionising sources turns on for expected scenarios. Hardening of the spectrum of the ionising radiation field due to passage through the high HI column densities leads to fluctuations in the f_HeII / f_HI ratio in the shadowed regions. These variations alone, however, do not reproduce the measured fluctuations. The post-ionisation temperature of the IGM provides strong constraints on the nature of the sources of reionisation.

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