2021ApJ...914...79T

Ultraluminous Lyα emitting galaxies (ULLAEs) with logL(Lyα)> 43.5 erg s^–1 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 deg² 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 active galactic nuclei at z = 5.7, an [O III]λ5007 emitter at z = 0.63, a red star, and two spectroscopic nondetections. Using the nine 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_–0.71^+1.12, which corresponds to an LF offset of 0.28_–0.20^+0.20 dex.