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

TL;DR

This study refines the understanding of cosmic reionization by combining multiple observational probes, showing a later and more extended reionization period consistent with Planck data and UV luminosity functions.

Contribution

It extends previous reionization models by allowing variation in UV source efficiency and testing less conservative UV luminosity function cuts, providing more flexible and constrained reionization histories.

Findings

Optical depth estimate remains consistent at τ≈0.052 with fixed efficiency.

Allowing efficiency variation does not significantly alter reionization timeline.

Less conservative UV cuts suggest a higher contribution from early, faint galaxies.

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 - 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 $\tau=0.0519_{-0.0008}^{+0.0010}$ at 68% CL , consistent with our previous studies. Using a less conservative cut for the UV luminosity function, we find $\tau=0.0541_{-0.0016}^{+0.0013}$ 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.