Reionization and galaxy inference from the high-redshift Ly{\alpha} forest

TL;DR

This paper presents a Bayesian framework to analyze high-redshift Ly{ extalpha} forests, constraining the epoch of reionization and galaxy properties, and providing insights into the timing and nature of the late reionization stages.

Contribution

It introduces a novel Bayesian forward-modeling approach to interpret Ly{ extalpha} forest data for reionization and galaxy property inference, incorporating priors from galaxy and CMB observations.

Findings

Overlap stages of EoR occur at z < 5.6.

Patchy reionization and UV background cause long Gunn-Peterson troughs.

Ionizing escape fraction is around 7-9%, with little evolution across galaxy masses.

Abstract

The transmission of Lyman-{\alpha} (Ly{\alpha}) in the spectra of distant quasars depends on the density, temperature, and ionization state of the intergalactic medium (IGM). Therefore, high-redshift (z > 5) Ly{\alpha} forests could be invaluable in studying the late stages of the epoch of reionization (EoR), as well as properties of the sources that drive it. Indeed, high-quality quasar spectra have now firmly established the existence of large-scale opacity fluctuations at z > 5, whose physical origins are still debated. Here we introduce a Bayesian framework capable of constraining the EoR and galaxy properties by forward-modelling the high-z Ly{\alpha} forest. Using priors from galaxy and CMB observations, we demonstrate that the final overlap stages of the EoR (when >95% of the volume was ionized) should occur at z < 5.6, in order to reproduce the large-scale opacity fluctuations seen in forest spectra. However, it is the combination of patchy reionization and the inhomogeneous UV background that produces the longest Gunn-Peterson troughs. Ly{\alpha} forest observations tighten existing constraints on the characteristic ionizing escape fraction of galaxies, with the combined observations suggesting f_{\rm esc} \approx 7^4_3%, and disfavoring a strong evolution with the galaxy's halo (or stellar) mass.