The deep2 galaxy redshift survey: First results on galaxy groups

Brian F. Gerke, Jeffrey A. Newman, Marc Davis, Christian Marinoni, Renbin Yan, Alison L. Coil, Charlie Conroy, Michael C. Cooper, S. M. Faber, Douglas P. Finkbeiner, Puragra Guhathakurta, Nick Kaiser, David C. Koo, Andrew C. Phillips, Benjamin J. Weiner, Christopher N.A. Willmer

Research output: Contribution to journalArticlepeer-review

113 Scopus citations


We use the first 25% of the DEEP2 Galaxy Redshift Survey spectroscopic data to identify groups and clusters of galaxies in redshift space. The data set contains 8370 galaxies with confirmed redshifts in the range 0.7 ≤ z ≤ 1.4, over 1 deg2 on the sky. Groups are identified using an algorithm (the Voronoi-Delaunay method) that has been shown to accurately reproduce the statistics of groups in simulated DEEP2-like samples. We optimize this algorithm for the DEEP2 survey by applying it to realistic mock galaxy catalogs and assessing the results using a stringent set of criteria for measuring group-finding success, which we develop and describe in detail here. We find in particular that the group finder can successfully identify ∼78% of real groups and that ∼79% of the galaxies that are true members of groups can be identified as such. Conversely, we estimate that ∼55% of the groups we find can be definitively identified with real groups and that ∼46% of the galaxies we place into groups are interloper field galaxies. Most importantly, we find that it is possible to measure the distribution of groups in redshift and velocity dispersion, n(σ, z), to an accuracy limited by cosmic variance, for dispersions greater than 350 km s-1. We anticipate that such measurements will allow strong constraints to be placed on the equation of state of the dark energy in the future. Finally, we present the first DEEP2 group catalog, which assigns 32% of the galaxies to 899 distinct groups with two or more members, 153 of which have velocity dispersions above 350 km s -1. We provide locations, redshifts and properties for this high-dispersion subsample. This catalog represents the largest sample to date of spectroscopically detected groups at z-1.

Original languageEnglish (US)
Pages (from-to)6-22
Number of pages17
JournalAstrophysical Journal
Issue number1 I
StatePublished - May 20 2005
Externally publishedYes


  • Galaxies: clusters: general
  • Galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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