Clusters of galaxies in the first half of the universe from the IRAC shallow survey

Peter R.M. Eisenhardt, Mark Brodwin, Anthony H. Gonzalez, S. Adam Stanford, Daniel Stern, Pauline Barmby, Michael J.I. Brown, Kyle Dawson, D. E.Y. Arjun, Mamoru Doi, Audrey Galametz, B. T. Jannuzi, C. S. Kochanek, Joshua Meyers, Tomoki Morokuma, Leonidas A. Moustakas

Research output: Contribution to journalReview articlepeer-review

220 Scopus citations


We have identified 335 galaxy cluster and group candidates, 106 of which are at z > 1, using a 4.5 μm-selected sample of objects from a 7.25 deg2 region in the Spitzer Infrared Array Camera (IRAC) Shallow Survey. Clusters were identified as three-dimensional overdensities using a wavelet algorithm, based on photometric redshift probability distributions derived from IRAC and NOAO Deep Wide-Field Survey data. We estimate only ∼10% of the detections are spurious. To date 12 of the z > 1 candidates have been confirmed spectroscopically, at redshifts from 1,06 to 1.41. Velocity dispersions of ∼750 km s-1 for two of these argue for total cluster masses well above 1014 M, as does the mass estimated from the rest-frame near-infrared stellar luminosity. Although not selected to contain a red sequence, some evidence for red sequences is present in the spectroscopically confirmed clusters, and brighter galaxies are systematically redder than the mean galaxy color in clusters at all redshifts. The mean 1 - [3.6] color for cluster galaxies up to z ∼ lis well matched by a passively evolving model in which stars are formed in a 0.1 Gyr burst starting at redshift zf = 3. At z > 1, a wider range of formation histories is needed, but higher formation redshifts (i.e., Zf > 3) are favored for most clusters.

Original languageEnglish (US)
Pages (from-to)905-932
Number of pages28
JournalAstrophysical Journal
Issue number2
StatePublished - Sep 10 2008


  • Galaxies: clusters: general
  • Surveys

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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