On the Use of Ly-alpha Emitters as Probes of Reionization

TL;DR

This study uses numerical simulations and a new Ly-alpha radiative transfer model to analyze how the patchy reionization of the intergalactic medium affects the observability of Ly-alpha emitters at high redshifts, providing insights into the timing of reionization.

Contribution

Introduces a novel model dividing Ly-alpha radiative transfer into galactic and extragalactic components to better understand IGM effects on LAE observability during reionization.

Findings

Rapid reionization scenario conflicts with other observations.

Two-point correlation function offers robust reionization constraints.

Predicted sample sizes for future observations to distinguish reionization models.

Abstract

We use numerical simulations to study the effects of the patchiness of a partly reionized intergalactic medium (IGM) on the observability of Ly-alpha emitters (LAEs) at high redshifts (z ~ 6). We present a new model that divides the Ly-alpha radiative transfer into a (circum-)galactic and an extragalactic (IGM) part, and investigate how the choice of intrinsic line model affects the IGM transmission results. We use our model to study the impact of neutral hydrogen on statistical observables such as the Ly-alpha restframe equivalent width (REW) distribution, the LAE luminosity function and the two-point correlation function. We find that if the observed changes in LAE luminosity functions and equivalent width distributions between z ~ 6 and z ~ 7 are to be explained by an increased IGM neutral fraction alone, we require an extremely late and rapid reionization scenario, where the Universe was ~ 40 % ionized at z = 7, ~ 50 % ionized at z = 6.5 and ~ 100 % ionized at z = 6. This is in conflict with other observations, suggesting that intrinsic LAE evolution at z > 6 cannot be completely neglected. We show how the two-point correlation function can provide more robust constraints once future observations obtain larger LAE samples, and provide predictions for the sample sizes needed to tell different reionization scenarios apart.