The Evolution of the Ultraluminous Ly-alpha Luminosity Function over z=5.7-6.6

TL;DR

This study constructs the luminosity function of ultraluminous Lyman alpha emitting galaxies at redshift 5.7, comparing it with the z=6.6 LF to understand their evolution during reionization.

Contribution

It provides the first spectroscopic luminosity function of ULLAEs at z=5.7 and compares it with higher redshift data to analyze evolutionary trends.

Findings

The number density of ULLAEs at z=5.7 is roughly twice that at z=6.6.

The ultraluminous end of the Lyman alpha LF shows mild evolution between these redshifts.

Spectroscopic confirmation of 9 ULLAEs at z=5.7 from a large survey.

Abstract

Ultraluminous Lyman alpha (Lya) emitting galaxies (ULLAEs) with log L (Lya)>43.5 erg/s near the epoch of reionization (z>5) make up the bright end of the LAE luminosity function (LF) and may provide insight into the process of reionization, including the formation of ionized bubbles around these extreme systems. We present a spectroscopic LF for ULLAEs at z=5.7. We used data from the HEROES ~45 sq. deg Subaru Hyper Suprime-Cam survey, which is centered on the North Ecliptic Pole and has both broadband (grizY) and narrowband (NB816 and NB921) imaging, to select candidate ULLAEs based on a NB816 excess and a strong broadband Lyman break. We spectroscopically observed 17 ULLAE candidates with DEIMOS on Keck II. We confirmed 12 as LAEs at z=5.7, 9 of which are ULLAEs. The remaining sources are an AGN at z=5.7, an [OIII]5007 emitter at z=0.63, a red star, and two spectroscopic non-detections. Using the 9 confirmed ULLAEs, we construct a ULLAE LF at z=5.7. After applying a comprehensive incompleteness correction, we compare our new z=5.7 LF with our recent z=6.6 LF and with other LFs from the literature to look for evolution at the ultraluminous end. We find the overall ratio of the z=5.7 to z=6.6 ULLAE comoving number densities to be 1.92 (+1.12, -0.71), which corresponds to a LF offset of 0.28 (+0.20, -0.20) dex.