The connection between high-redshift galaxies and Lyman α transmission in the Sherwood–Relics simulations of patchy reionization

ABSTRACT Recent work has suggested that, during reionization, spatial variations in the ionizing radiation field should produce enhanced Ly forest transmission at distances of tens of comoving Mpc from high-redshift galaxies. We demonstrate that the Sherwood–Relics suite of hybrid radiation-hydrodynamical simulations are qualitatively consistent with this interpretation. The shape of the galaxy–Ly transmission cross-correlation is sensitive to both the mass of the haloes hosting the galaxies and the volume averaged fraction of neutral hydrogen in the IGM, x ₇\, ₈. The reported excess Ly forest transmission on scales r 10~ cMpc at z 5. 2 – as measured using C iv absorbers as proxies for high-redshift galaxies – is quantitatively reproduced by Sherwood–Relics at z=6 if we assume the galaxies that produce ionizing photons are hosted in haloes with mass M ₇ 10^10~h^-1\, M_. However, this redshift mismatch is equivalent to requiring x ₇\, ₈ 0. 1 at z 5. 2, which is inconsistent with the observed Ly forest effective optical depth distribution. We suggest this tension may be partly resolved if the minimum C iv absorber host halo mass at z5 is larger than M ₇=10^10~h^-1\, M_. After reionization completes, relic IGM temperature fluctuations will continue to influence the shape of the cross-correlation on scales of a few comoving Mpc at 4 z 5. Constraining the redshift evolution of the cross-correlation over this period may therefore provide further insight into the timing of reionization.