Passive galaxies as tracers of cluster environments at z ~ 2

V. Strazzullo, E. Daddi, RAPHAEL ALEXANDRE SIMON GOBAT , B. Garilli, M. Mignoli, F. Valentino, M. Onodera, A. Renzini, A. Cimatti, A. Finoguenov, N. Arimoto, M. Cappellari, C. M. Carollo, C. Feruglio, E. Le Floc'h, S. J. Lilly, D. MacCagni, H. J. McCracken, M. Moresco, L. PozzettiG. Zamorani

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Even 10 billion years ago, the cores of the first galaxy clusters are often found to host a characteristic population of massive galaxies with already suppressed star formation. Here we search for distant cluster candidates at z ~ 2 using massive passive galaxies as tracers. With a sample of ~40 spectroscopically confirmed passive galaxies at 1.3 < z < 2.1, we tuned photometric redshifts of several thousand passive sources in the 2 sq. deg COSMOS field. This allowed us to map their density in redshift slices, probing the large-scale structure in the COSMOS field as traced by passive sources. We report here on the three strongest passive galaxy overdensities that we identify in the range 1.5 < z < 2.5. While the actual nature of these concentrations still needs to be confirmed, we discuss their identification procedure and the arguments supporting them as candidate galaxy clusters (probably in the mid-10 13 M range). Although this search approach is probably biased toward more evolved structures, it has the potential of selecting still rare, cluster-like environments close to their epoch of first appearance, enabling new investigations of the evolution of galaxies in the context of structure growth.

Original languageEnglish
JournalAstronomy and Astrophysics
StatePublished - 1 Apr 2015


  • Galaxies: clusters: general
  • Galaxies: high-redshift
  • Large-scale structure of Universe

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