Extended red wings and the visibility of reionization-epoch Lyman-α emitters

Abstract

Abstract The visibility of the Lyman-α (Lyα) emission from reionization-epoch galaxies depends sensitively on the extent of the intrinsic Lyα emission redwards of 1215.67 Å. The prominent red peak resulting from resonant radiative transfer in the interstellar medium is often modelled as a single Gaussian. We use the Azahar simulation suite of a massive-reionization epoch galaxy to show that a significantly larger fraction of the Lyα emission extends to 400-800 km s−1, and thus significantly further to the red than predicted by a Gaussian line profile. A cycle of frequent galaxy mergers strongly modulates the Lyα luminosity, the red peak velocity and its extended red wing emerging from the galaxy, which all also strongly vary with viewing angle. The Lyα emission also depends sensitively on the implemented feedback, dust and star formation physics. Our simulations including cosmic rays reproduce the observed spectral properties of reionization epoch Lyα emitters (LAEs) well if we assume that the Lyα emission is affected by very little dust. The visibility of LAEs can be strongly underestimated if the extended red wings of the intrinsic Lyα emission are not accounted for. We discuss implications for using the visibility of LAEs to constrain the evolution of the volume-averaged neutral fraction during reionization.