SILVERRUSH. VII. Subaru/HSC Identifications of 42 Protocluster Candidates at z~6-7 with the Spectroscopic Redshifts up to z=6.574: Implications for Cosmic Reionization

We report fourteen and twenty-eight protocluster candidates at z = 5 . 7 and 6 . 6 over 14 and 19 deg 2 areas, respectively, selected from 2,230 (259) Ly α emitters (LAEs) photometrically (spectroscopically) identified with Subaru/Hyper Suprime-Cam (HSC) deep images (Keck, Subaru, and Magellan spectra and the literature data). Six out of the 42 protocluster candidates include 1 − 12 spectroscopically confirmed LAEs at redshifts up to z = 6 . 574. By the comparisons with the cosmological Ly α radiative transfer (RT) model reproducing LAEs with the reionization effects, we find that more than a half of these protocluster candidates are progenitors of the present-day clusters with a mass of & 10 14 M ⊙ . We then investigate the correlation between LAE overdensity δ and Ly α rest-frame equivalent width EW restLy α , because the cosmological Ly α RT model suggests that a slope of EW restLy α - δ relation is steepened towards the epoch of cosmic reionization (EoR), due to the existence of the ionized bubbles around galaxy overdensities easing the escape of Ly α emission from the partly neutral intergalactic medium (IGM). The available HSC data suggest that the slope of the EW restLy α - δ correlation does not evolve from the post-reionization epoch z = 5 . 7 to the EoR z = 6 . 6 beyond the moderately large statistical errors. There is a possibility that we would detect the evolution of the EW restLy α - δ relation from z = 5 . 7 to 7 . 3 by the upcoming HSC observations providing large samples of LAEs at z = 6 . 6 − 7 . 3.