The Detectability of Lyman Alpha Emission from Galaxies during the Epoch of Reionization

TL;DR

This study models the transmission of Lyman Alpha emission from high-redshift galaxies during the Epoch of Reionization, showing that strong emission can occur even in a highly neutral universe, with implications for understanding reionization.

Contribution

It combines galactic outflow models with large-scale simulations to quantify Lyman Alpha photon transmission during reionization, providing new insights into galaxy visibility in the early universe.

Findings

Winds increase Lya transmission even in neutral IGM.

Strong Lya emission observed at z=8.6 is consistent with a highly neutral universe.

Rapid evolution in neutral hydrogen fraction is needed to explain drop in LAE fraction.

Abstract

We study the visibility of the Lyman Alpha (Lya) emission line during the Epoch of Reionization (EoR). Combining galactic outflow models with large-scale semi-numeric simulations of reionization, we quantify the probability distribution function (PDF) of the fraction of Lya photons transmitted through the intergalactic medium (IGM), T_IGM. Our study focusses on galaxies populating dark matter halos with masses of M_halo=1e10 M_sun at z=8.6, which is inspired by the recent reported discovery of a galaxy at z=8.6 with strong Lya line emission. For reasonable model assumptions, we find that winds cause T_IGM>10% [50%], for the majority of galaxies, even when the Universe is ~80% [60%] neutral by volume. Thus, the observed strong Lya emission from the reported z=8.6 galaxy is consistent with a highly neutral IGM. We also investigate the implications of the recent tentative evidence for a observed decrease in the `LAE fraction' among drop-out galaxies between z=6 and z=7. If confirmed, we show that a rapid evolution in x_HI will be required to explain this observation via the effects of reionization.