The Ultraluminous Lyα Luminosity Function at z = 6.6

We present the luminosity function (LF) for ultraluminous Ly α emitting galaxies (LAEs) at z = 6.6. We define ultraluminous LAEs (ULLAEs) as galaxies with erg s −1 . We select our main sample using the g ′, r ′, i ′, z ′, and NB921 observations of a wide-area (30 deg 2 ) Hyper Suprime-Cam survey of the north ecliptic pole (NEP) field. We select candidates with , NB921 ≤ 23.5, and . Using the DEIMOS spectrograph on Keck II, we confirm 9 of our 14 candidates as ULLAEs at z = 6.6 and the remaining 5 as an active galactic nucleus at z = 6.6, two [O iii ] λ 5007 emitting galaxies at z = 0.84 and z = 0.85, and two nondetections. This emphasizes the need for full spectroscopic follow-up to determine accurate LFs. In constructing the ULLAE LF at z = 6.6, we combine our nine NEP ULLAEs with two previously discovered and confirmed ULLAEs in the COSMOS field: CR7 and COLA1. We apply rigorous corrections for incompleteness based on simulations. We compare our ULLAE LF at z = 6.6 with LFs at z = 5.7 and z = 6.6 from the literature. Our data reject some previous LF normalizations and power-law indices, but they are broadly consistent with others. Indeed, a comparative analysis of the different literature LFs suggests that no LF is fully consistent with any of the others, making it critical to determine the evolution from z = 5.7 to z = 6.6 using LFs constructed in exactly the same way at both redshifts.