Thermal constraints on the reionisation of hydrogen by population-II stellar sources

TL;DR

This study uses recent high-redshift quasar temperature measurements and a semi-numerical model to constrain the epoch of hydrogen reionisation, indicating it was completed by redshift z > 7.9 with current data.

Contribution

It introduces a novel method combining IGM temperature data with inhomogeneous reionisation modeling to constrain reionisation timing at z > 6.

Findings

Reionisation completed by z > 7.9 at 68% confidence.

Temperature measurements at z ~ 6 constrain reionisation history.

Future data will further tighten these constraints.

Abstract

Measurements of the intergalactic medium (IGM) temperature provide a potentially powerful constraint on the reionisation history due to the thermal imprint left by the photo-ionisation of neutral hydrogen. However, until recently IGM temperature measurements were limited to redshifts 2 < z < 4.8, restricting the ability of these data to probe the reionisation history at z > 6. In this work, we use recent measurements of the IGM temperature in the near-zones of seven quasars at z ~ 5.8 - 6.4, combined with a semi-numerical model for inhomogeneous reionisation, to establish new constraints on the redshift at which hydrogen reionisation completed. We calibrate the model to reproduce observational constraints on the electron scattering optical depth and the HI photo-ionisation rate, and compute the resulting spatially inhomogeneous temperature distribution at z ~ 6 for a variety of reionisation scenarios. Under standard assumptions for the ionising spectra of population-II sources, the near-zone temperature measurements constrain the redshift by which hydrogen reionisation was complete to be z > 7.9 (6.5) at 68 (95) per cent confidence. We conclude that future temperature measurements around other high redshift quasars will significantly increase the power of this technique, enabling these results to be tightened and generalised.