SILVERRUSH. VII. Subaru/HSC Identifications of Protocluster Candidates at z ∼ 6-7: Implications for Cosmic Reionization

• Published in: The Astrophysical journal 2019-07, Vol.879 (1), p.28
• Main Authors: Higuchi, Ryo, Ouchi, Masami, Ono, Yoshiaki, Shibuya, Takatoshi, Toshikawa, Jun, Harikane, Yuichi, Kojima, Takashi, Chiang, Yi-Kuan, Egami, Eiichi, Kashikawa, Nobunari, Overzier, Roderik, Konno, Akira, Inoue, Akio K., Hasegawa, Kenji, Fujimoto, Seiji, Goto, Tomotsugu, Ishikawa, Shogo, Ito, Kei, Komiyama, Yutaka, Tanaka, Masayuki
• Format: Article
• Language: English
• Subjects: Astrophysics; Computer simulation; Correlation; Emitters; Galaxies; galaxies: evolution; galaxies: formation; galaxies: high-redshift; Intergalactic media; Ionization; Radiative transfer; Rest; Slopes; Statistical methods
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab2192

We report 14 and 26 protocluster candidates at z = 5.7 and 6.6 over 14 and 16 deg2 areas, respectively, selected from 2230 (259) Ly emitters (LAEs) photometrically (spectroscopically) identified using Subaru/Hyper Suprime-Cam (HSC) deep images (Keck, Subaru, and Magellan spectra, and literature data). Six out of the 40 protocluster candidates include one to 13 spectroscopically confirmed LAEs. We conduct Monte Carlo simulations to estimate how many protocluster candidates are found by chance for randomly distributed sources, and find that the effective number of protocluster candidates at z = 5.7 (6.6) is six (five). By comparing with the cosmological Ly radiative transfer (RT) model reproducing the LAEs with reionization effects, we find that more than half of these protocluster candidates are progenitors of present-day clusters with mass of . We then investigate the correlation between the LAE overdensity δ and the Ly rest-frame equivalent width , because the cosmological Ly RT model suggests that the slope of the -δ relation steepens toward the epoch of cosmic reionization (EoR), due to the existence of ionized bubbles around galaxy overdensities easing the escape of Ly emission from the partly neutral intergalactic medium. The available HSC data suggest that the slope of the -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 could detect the evolution of the -δ relation from z = 5.7 to 7.3 using the upcoming HSC observations that will provide large samples of LAEs at z = 6.6-7.3.