COSMOS2020: Identification of High-z Protocluster Candidates in COSMOS

Malte Brinch, Thomas R. Greve, John R. Weaver, Gabriel Brammer, Olivier Ilbert, Marko Shuntov, Shuowen Jin, Daizhong Liu, Clara Giménez-Arteaga, Caitlin M. Casey, Iary Davidson, Seiji Fujimoto, Anton M. Koekemoer, Vasily Kokorev, Georgios Magdis, H. J. McCracken, Conor J. R. McPartland, Bahram Mobasher, David B. Sanders, Sune ToftFrancesco Valentino, Giovanni Zamorani

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We conduct a systematic search for protocluster candidates at z ≥ 6 in the Cosmic Evolution Survey (COSMOS) field using the recently released COSMOS2020 source catalog. We select galaxies using a number of selection criteria to obtain a sample of galaxies that have a high probability of being inside a given redshift bin. We then apply overdensity analysis to the bins using two density estimators, a Weighted Adaptive Kernel estimator and a Weighted Voronoi Tessellation estimator. We have found 15 significant (>4σ) candidate galaxy overdensities across the redshift range 6 ≤ z ≤ 7.7. The majority of the galaxies appear to be on the galaxy main sequence at their respective epochs. We use multiple stellar-mass-to-halo-mass conversion methods to obtain a range of dark matter halo mass estimates for the overdensities in the range of ∼1011–1013 M ⊙, at the respective redshifts of the overdensities. The number and the masses of the halos associated with our protocluster candidates are consistent with what is expected from the area of a COSMOS-like survey in a standard Λ cold dark matter cosmology. Through comparison with simulation, we expect that all of the overdensities at z ≃ 6 will evolve into Virgo-/Coma-like clusters at present (i.e., with masses ∼1014–1015 M ⊙). Compared to other overdensities identified at z ≥ 6 via narrowband selection techniques, the overdensities presented appear to have ∼10× higher stellar masses and star formation rates (SFRs). We compare the evolution in the total SFR and stellar mass content of the protocluster candidates across the redshift range 6 ≤ z ≤ 7.7 and find agreement with the total average SFR from simulations.
Original languageEnglish
Article number153
JournalAstrophysical Journal
Issue number2
Number of pages47
Publication statusPublished - 2023


  • High-redshift galaxy clusters
  • Galaxy evolution
  • Large-scale structure of the universe


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