Ly-{alpha} correlation with 67 QSOs at 5<z<6.1

We perform an MCMC analysis to quantify the extent and strength of the correlation, making use of several functional forms. We moreover employ new large-volume (1.5^3^Gpc^3^) light-cones of Lyman-{alpha} transmission implementing different reionization scenarios to interpret the observed signal, including a fiducial box employing SCRIPT. We detect strong correlations at redshifts z>5.3, extending at least tens of Mpc and strongly increasing with redshift.

Our results suggest a redshift-dependent correlation length, from L<=26.53(68.47)Mpc at 1-{sigma} (2-{sigma}) limit at redshift z=5.0 to L=252.72^+272.61^_-41.61_Mpc at redshift z=6.1. On the contrary, our simulations all demonstrate characteristic correlation scales <60Mpc with a very slow redshift evolution, in strong tension with our observations. The presence and redshift-dependence of correlations in the Lyman-{alpha} forest on >200Mpc scales at z=6 indicates that cosmological simulations should be larger than this scale to adequately sample the Lyman-{alpha} forest.

Despite implementing a fluctuating UVB and numerous neutral islands at z<6, and matching well the sightline scatter in the Lyman-{alpha} forest, our fiducial SCRIPT- based simulation fails to reproduce the large-scale correlations. It may be that those ingredients are necessary, but not sufficient, to understanding the unfolding of the EoR.