Lyman Alpha Emitters at Redshift z=5.7

TL;DR

This study identifies Lyman alpha emitters at redshift 5.7, providing insights into early galaxy formation and the epoch of reionization, and compares their properties to those at redshift 4.5.

Contribution

First photometric sample of z=5.7 Lyman alpha emitters, constraining reionization redshift and galaxy evolution models.

Findings

Presence of low-luminosity Lyman alpha sources at z=5.7 implies reionization occurred after this epoch.

Number of z=5.7 emitters exceeds no-evolution models but is below some theoretical predictions.

Equivalent width distribution similar at z=4.5 and z=5.7, indicating young, first-generation star-forming galaxies.

Abstract

Lyman alpha galaxies at high redshifts offer a powerful probe of both the formation of galaxies and the reionization of the intergalactic medium. Lyman alpha line emission is an efficient tool for identifying young galaxies at high redshift, because it is strong in systems with young stars and little or no dust-- properties expected in galaxies undergoing their first burst of star-formation. Lyman alpha galaxies also provide a robust test of the reionization epoch that is independent of Gunn-Peterson trough observations in quasar spectra and is better able to distinguish line center optical depths tau=5 from tau=10^5. This is because neutral gas scatters Lyman alpha photons, dramatically ``blurring'' images of Lyman alpha galaxies embedded in a neutral intergalactic medium and rendering them undetectable. We present a photometrically selected sample of z=5.7 Lyman alpha emitters derived from the Large Area Lyman Alpha survey. The presence of these low-luminosity Lyman alpha sources at z=5.7 immediately implies that the reionization redshift was > 5.7. Comparing these objects to our earlier z=4.5 sample, we find that the number of z=5.7 emitters at fixed line luminosity marginally exceeds the no-evolution expectation, but falls well short of published model predictions. The equivalent width distribution is similar at the two redshifts. The large equivalent widths of the Lyman alpha line indicate young galaxies undergoing their first star formation.