First results from Z-FOURGE: discovery of a candidate cluster at z = 2.2 in COSMOS

Lee R. Spitler*, Ivo Labbé, Karl Glazebrook, S. Eric Persson, Andy Monson, Casey Papovich, Kim Vy H Tran, Gregory B. Poole, Ryan Quadri, Pieter Van Dokkum, Daniel D. Kelson, Glenn G. Kacprzak, Patrickj McCarthy, David Murphy, Caroline M S Straatman, Vithal Tilvi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

100 Citations (Scopus)


We report the first results from the Z -FOURGE survey: the discovery of a candidate galaxy cluster at z = 2.2 consisting of two compact overdensities with red galaxies detected at ≳ 20σ above the mean surface density. The discovery was made possible by a new deep (Ks ≲ 24.8 AB 5σ) Magellan/FOURSTAR near-IR imaging survey with five custom medium-bandwidth filters. The filters pinpoint the location of the Balmer/4000 break in evolved stellar populations at 1.5 < z < 3.5, yielding significantly more accurate photometric redshifts than possible with broadband imaging alone. The overdensities are within 1′ of each other in the COSMOS field and appear to be embedded in a larger structure that contains at least one additional overdensity (10σ). Considering the global properties of the overdensities, the z = 2.2 system appears to be the most distant example of a galaxy cluster with a population of red galaxies. A comparison to a large ΛCDM simulation suggests that the system may consist of merging subclusters, with properties in between those of z > 2 protoclusters with more diffuse distributions of blue galaxies and the lower-redshift galaxy clusters with prominent red sequences. The structure is completely absent in public optical catalogs in COSMOS and only weakly visible in a shallower near-IR survey. The discovery showcases the potential of deep near-IR surveys with medium-band filters to advance the understanding of environment and galaxy evolution at z > 1.5.

Original languageEnglish
Article numberL21
Pages (from-to)1-6
Number of pages6
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 1 Apr 2012
Externally publishedYes


Dive into the research topics of 'First results from Z-FOURGE: discovery of a candidate cluster at z = 2.2 in COSMOS'. Together they form a unique fingerprint.

Cite this