Dark Twilight Joined with the Light of Dawn to Unveil the Reionization History

Abstract

Improved measurement of the Cosmic Microwave Background polarization from Planck allows a detailed study of reionization beyond the average optical depth. The lower value of the optical depth disfavours an early onset and an early completion of reionization in favour of a redsfhit range where different astrophysical probes provide sensible information on the sources of reionization and the status of the intergalactic medium. In this work we extend our previous study in which we constrained reionization by combining three different probes -CMB, UV luminosity density and neutral hydrogen fraction data [1] -in both treatment and data: we first allow variation in the UV source term varying the product of the efficiency of conversion of UV luminosity into ionizing photons and the escape fraction together with the reionization and cosmological parameters, and then we investigate the impact of a less conservative cut for the UV luminosity function. We find that the estimate for the efficiency is consistent within 95% C.L. with the fixed value we considered in our previous results and is mostly constrained by the QHII data. We find that allowing the efficiency to vary does not affect significantly our results for the average optical depth for monotonic reionization histories, recovering τ = 0.0519 +0.0010 −0.0008 at 68 %CL , consistent with our previous studies. Using a less conservative cut for the UV luminosity function, we find τ = 0.0541 +0.0013 −0.0016 at 68 % CL, due to the faint end of the luminosity function in the data we use, that also prefers a larger contribution from higher redshifts.