GOLDRUSH. III. A systematic search for protoclusters at z ∼ 4 based on the >100 deg2 area

Jun Toshikawa, Hisakazu Uchiyama, Nobunari Kashikawa, Masami Ouchi, Roderik Overzier, Yoshiaki Ono, Yuichi Harikane, Shogo Ishikawa, Tadayuki Kodama, Yuichi Matsuda, Yen Ting Lin, Masafusa Onoue, Masayuki Tanaka, Tohru Nagao, Masayuki Akiyama, Yutaka Komiyama, Tomotsugu Goto, Chien Hsiu Lee

Research output: Contribution to journalArticlepeer-review

56 Citations (Scopus)


We conduct a systematic search for galaxy protoclusters at z ∼ 3.8 based on the latest internal data release (S16A) of the Hyper Suprime-Cam Subaru strategic program (HSCSSP). In the Wide layer of the HSC-SSP, we investigate the large-scale projected sky distribution of g-dropout galaxies over an area of 121 deg2, and identify 216 large-scale overdense regions (>4 σ overdensity significance) that are likely protocluster candidates. Of these, 37 are located within 8 (3.4 physical Mpc) of other protocluster candidates of higher overdensity, and are expected to merge into a single massive structure by z = 0. Therefore, we find 179 unique protocluster candidates in our survey. A cosmological simulation that includes projection effects predicts that more than 76% of these candidates will evolve into galaxy clusters with halo masses of at least 1014 M by z = 0. The unprecedented size of our protocluster candidate catalog allows us to perform, for the first time, an angular clustering analysis of the systematic sample of protocluster candidates. We find a correlation length of 35.0 h-1 Mpc. The relation between correlation length and number density of z ∼ 3.8 protocluster candidates is consistent with the prediction of the ΣCDM model, and the correlation length is similar to that of rich clusters in the local universe. This result suggests that our protocluster candidates are tracing similar spatial structures to those expected from the progenitors of rich clusters, and enhances the confidence that our method for identifying protoclusters at high redshifts is robust. In years to come, our protocluster search will be extended to the entire HSC-SSP Wide sky coverage of ∼1400 deg2 to probe cluster formation over a wide redshift range of z ∼ 2-6.

Original languageEnglish
Article numberS12
JournalPublications of the Astronomical Society of Japan
Issue numberSpecial Issue 1
Publication statusPublished - 2018 Jan 1
Externally publishedYes


  • Evolution-galaxies
  • Formation-galaxies
  • Galaxies
  • High-redshift-large-scale structure of universe

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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