2020ApJ...896..156F

We present 36 spectroscopically confirmed intrinsically UV-faint Lyα-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 0.001L*. We identified 19 high-confidence detections and 17 likely detections of Lyα. 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 Lyα emission and the photometric redshifts of the nondetections. Considering only objects where Lyα could be detected at EW(Lyα) > 25 Å at 3σ at the fiducial depth of our survey, and only those galaxies with EW(Lyα) > 25 Å, and only objects with m_AB < 26.8, we found the Lyα 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 Lyα 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.