Photo-heating and the fate of hard photons during the reionisation of HeII by quasars

Understand

We use a combination of analytic and numerical arguments to consider the impact of quasar photo-heating during HeII reionisation on the thermal evolution of the intergalactic medium (IGM).

• We demonstrate that rapid (\Delta z< 0.1-0.2), strong (\Delta T > 10^4 K) photo-heating is difficult to achieve across the entire IGM unless quasar spectra are significantly harder than implied by current observational constraints.
• Although filtering of intrinsic quasar radiation through dense regions in the IGM does increase the mean excess energy per HeII photo-ionisation, it also weakens the radiation intensity and lowers the photo-ionisation rate, preventing rapid heating over time intervals shorter than the local photo-ionisation timescale.
• Moreover, the hard photons responsible for the strongest heating are more likely to deposit their energy inside dense clumps.