Subaru/HSC identifications of protocluster candidates at z ∼ 6-7: Implications for cosmic reionization

Ryo Higuchi, Masami Ouchi, Yoshiaki Ono, Takatoshi Shibuya, Jun Toshikawa, Yuichi Harikane, Takashi Kojima, Yi Kuan Chiang, Eiichi Egami, Nobunari Kashikawa, Roderik Overzier, Akira Konno, Akio K. Inoue, Kenji Hasegawa, Seiji Fujimoto, Tomotsugu Goto, Shogo Ishikawa, Kei Ito, Yutaka Komiyama, Masayuki Tanaka

Research output: Contribution to journalArticlepeer-review


We report fourteen and twenty-eight protocluster candidates at z = 5.7 and 6.6 over 14 and 19 deg2 areas, respectively, selected from 2,230 Lyα emitters (LAEs) photometrically identified with Subaru/Hyper Suprime-Cam (HSC) deep images. Six out of the 42 protocluster candidates include at least 1 spectroscopically confirmed LAEs at redshifts up to z = 6.574. By the comparisons with the cosmological Lyα radiative transfer (RT) model reproducing LAEs with the reionization effects, we find that more than a half of these protocluster candidates might be progenitors of the present-day clusters with a mass of 3 1014M . We also investigate the correlation between LAE overdensity and Lya rest-frame equivalent width (EW), because the cosmological Lyα RT model suggests that a slope of EW-overdensity 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 Lyα emission from the partly neutral intergalactic medium. The available HSC data suggest that the slope of the EW-overdensity correlation does not evolve from the post-reionization epoch z = 5.7 to the EoR z = 6.6 beyond the moderately large statistical errors.

Original languageEnglish (US)
Pages (from-to)231-234
Number of pages4
JournalProceedings of the International Astronomical Union
Issue numberS341
StatePublished - 2019


  • galaxies: evolution
  • galaxies: formation
  • galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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