Redshift Evolution of Galaxy Cluster Densities
Abstract
The number of rich galaxy clusters per unit volume is a strong function of Ω, the cosmological density parameter, and σ_{8}, the linear extrapolation to z = 0 of the density contrast in 8 h^{1} Mpc spheres. The Canadian Network for Observational Cosmology (CNOC) cluster redshift survey provides a sample of clusters, the average mass profiles of which are accurately known, which enables a secure association between cluster numbers and the filtered density perturbation spectrum. We select from the CNOC cluster survey those Extended MediumSensitivity Survey clusters with bolometric L_{X} >= 10^{45} ergs s^{1} and a velocity dispersion exceeding 800 km s^{1} in the redshift ranges 0.180.35 and 0.350.55. We compare the number density of these subsamples with similar samples at both high and low redshift. Using the PressSchechter formalism and cold dark matter (CDM) style structure models, the density data are best described with σ_{8} ~= 0.75 +/ 0.1 and Ω ~= 0.4 +/ 0.2 (90% confidence). The cluster dynamical analysis gives Ω = 0.2 +/ 0.1 for which σ_{8} = 0.95 +/ 0.1 (90% confidence). The predicted cluster density evolution in an Ω = 1 CDM model exceeds that observed by more than 1 order of magnitude.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1997
 DOI:
 10.1086/310577
 arXiv:
 arXiv:astroph/9612169
 Bibcode:
 1997ApJ...479L..19C
 Keywords:

 GALAXIES: CLUSTERS: GENERAL;
 COSMOLOGY: LARGESCALE STRUCTURE OF UNIVERSE;
 cosmology: largescale structure of universe;
 galaxies: clusters;
 Astrophysics
 EPrint:
 Revised version accepted for publication in ApJLetts. 10 pages. Also available at http://manaslu.astro.utoronto.ca/~carlberg/cnoc/sigma8/s8.ps.gz