{
  "id": "astro-ph/9706018",
  "version": "v1",
  "published": "1997-06-03T02:55:24.000Z",
  "updated": "1997-06-03T02:55:24.000Z",
  "title": "Constraining Omega with Cluster Evolution",
  "authors": [
    "Neta A. Bahcall",
    "Xiaohui Fan",
    "Renyue Cen"
  ],
  "comment": "14 pages, 3 Postscript figures, ApJ Letters, accepted",
  "journal": "Astrophys.J. 485 (1997) L53",
  "doi": "10.1086/310814",
  "categories": [
    "astro-ph"
  ],
  "abstract": "We show that the evolution of the number density of rich clusters of galaxies breaks the degeneracy between Omega (the mass density ratio of the universe) and sigma_{8} (the normalization of the power spectrum), sigma_{8}Omega^{0.5} \\simeq 0.5, that follows from the observed present-day abundance of rich clusters. The evolution of high-mass (Coma-like) clusters is strong in Omega=1, low-sigma_{8} models (such as the standard biased CDM model with sigma_{8} \\simeq 0.5), where the number density of clusters decreases by a factor of \\sim 10^{3} from z = 0 to z \\simeq 0.5; the same clusters show only mild evolution in low-Omega, high-sigma_{8} models, where the decrease is a factor of \\sim 10. This diagnostic provides a most powerful constraint on Omega. Using observations of clusters to z \\simeq 0.5-1, we find only mild evolution in the observed cluster abundance. We find Omega = 0.3 \\pm 0.1 and sigma_{8} = 0.85 \\pm 0.15 (for Lambda = 0 models; for Omega + Lambda = 1 models, Omega = 0.34 \\pm 0.13). These results imply, if confirmed by future surveys, that we live in a low-den sity, low-bias universe.",
  "revisions": [
    {
      "version": "v1",
      "updated": "1997-06-03T02:55:24.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cluster evolution",
      "constraining omega",
      "number density",
      "rich clusters",
      "mild evolution"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 461408
    }
  }
}