The thermal proximity effect around high redshift quasars

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The thermal state of the intergalactic medium (IGM) provides an indirect probe of both the H-I and He-II reionisation epochs. However, the very late reionisation models ending at z~5.3 favoured by Lyman-alpha forest observations and Lyman-alpha emitter clustering are in tension with IGM temperature constraints from quasar proximity zones at z~6; the latter prefer (at 95% confidence) that reionisation completes at z>6.5. Hence, either there are problems with the IGM temperature measurements at z>6, or the cold IGM around these high redshift quasars presents a challenge to the currently favoured very late reionisation models. The goal of this project will be to revisit measurements of the IGM temperature around z>5 quasars. This will use the Sherwood-Relics simulations, combined with radiative transfer modelling and archival echelle spectra of Lyman-alpha absorption. The timing of reionisation and the relative contribution of sources with non-thermal spectra to the reionisation photon budget will be addressed.