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

We present the Ly alpha luminosity function (LF) derived from 34 Ly alpha emitters (LAEs) at z = 7.0 on an area of sky of 3.1 deg(2), the largest sample of those in the literature to date obtained at a redshift z greater than or similar to 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 Ly alpha 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 Ly alpha LF from the faint end to the bright end. We find that the shape of the z = 7.0 Ly alpha LF can be explained by the steep slope of alpha similar or equal to -2.5 suggested at z = 6.6, and that there is no clear signature of a bright-end excess at z similar or equal to 7 claimed by the previous work, which was thought to be created by the ionized bubbles around bright LAEs, whose Ly alpha photons could easily escape from the partly neutral intergalactic medium (IGM) at z similar or equal to 7. We estimate the Ly alpha luminosity densities (LDs) with Ly alpha LFs at z similar or equal to 6-8 given by our studies and the previous ones, and compare the evolution of the UV-continuum LD estimated with dropouts. The Ly alpha LD monotonically decreases from z similar to 6 to 8, and evolves more strongly than the UV-continuum LD, which is indicative of the Ly alpha damping wing absorption of the IGM toward the heart of the reionization epoch.