CHORUS. II. Subaru/HSC Determination of the Lyα Luminosity Function at z = 7.0: Constraints on Cosmic Reionization Model Parameter

We present the Lyα luminosity function (LF) derived from 34 Lyα emitters (LAEs) at z = 7.0 on an area of sky of 3.1 deg², the largest sample of those in the literature to date obtained at a redshift z 7. The LAE sample is compiled from deep large-area narrowband observations with Subaru conducted by the Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) project. The z = 7.0 Lyα LF of our project is consistent with those of the previous Dark Energy Camera and Subaru studies at the bright and faint ends, respectively, while having uncertainties that are significantly smaller than those of the previous study results. Exploiting the small errors of our measurements, we investigate the shape of the Lyα LF from the faint end to the bright end. We find that the shape of the z = 7.0 Lyα LF can be explained by the steep slope of α ≃ -2.5 suggested at z = 6.6, and that there is no clear signature of a bright-end excess at z ≃ 7 claimed by the previous work, which was thought to be created by the ionized bubbles around bright LAEs, whose Lyα photons could easily escape from the partly neutral intergalactic medium (IGM) at z ≃ 7. We estimate the Lyα luminosity densities (LDs) with Lyα LFs at z ≃ 6-8 given by our studies and the previous ones, and compare the evolution of the UV-continuum LD estimated with dropouts. The Lyα LD monotonically decreases from z ∼ 6 to 8, and evolves more strongly than the UV-continuum LD, which is indicative of the Lyα damping wing absorption of the IGM toward the heart of the reionization epoch.