Spectroscopically Confirmed Lyα Emitters from Redshift 5 to 7 behind 10 Galaxy Cluster Lenses

Abstract

We present 36 spectroscopically confirmed intrinsically UV-faint Ly α -emitting galaxies from follow-up observations with Keck/DEep Imaging Multi-Object Spectrograph of gravitationally lensed high-redshift candidates. Candidates were selected to be between 5 ≲  z  ≲ 7 from photometric data using Hubble Space Telescope and Spitzer imaging surveys. We performed an integrated photometric redshift probability cut >1% between 5 <  z  < 7 to construct a sample of 198 high-redshift objects. Our sample spans intrinsic UV luminosities from a few L * down to 0.001 L *. We identified 19 high-confidence detections and 17 likely detections of Ly α . We divided our sample into lower-redshift ( z  ∼ 5.5) and higher-redshift ( z  ∼ 6.5) bins and ran Monte Carlo trials, incorporating the strengths of the Ly α emission and the photometric redshifts of the nondetections. Considering only objects where Ly α could be detected at EW(Ly α ) > 25 Å at 3 σ  at the fiducial depth of our survey, and only those galaxies with EW(Ly α ) > 25 Å, and only objects with m AB  < 26.8, we found the Ly α emitter (LAE) fraction to be flat or modestly increase from 0.26 ± 0.04 to 0.30 ± 0.04. These values are consistent with a rising LAE fraction with redshift out to z  ∼ 6, but at z  ∼ 6.5, there is some tension between our results and results from surveys at intrinsically brighter luminosities. We conclude that intrinsically fainter galaxies have Ly α emission, and there is a steep drop in the LAE fraction from our high-redshift sample at z  ∼ 6.5 and from similar galaxies at z  ∼ 7.5. This likely indicates we are witnessing the tail end of the epoch of reionization, as such a drop is not expected due to changes of intrinsic galaxy properties between these redshifts.