ar X iv : a st ro - p h / 97 03 10 7 v 2 2 3 M ay 1 99 7 The Average Mass Profile of Galaxy Clusters

The average mass density profile measured in the CNOC cluster survey is well described with the analytic form ρ(r) = Ar(r + aρ) , as advocated on the basis on n-body simulations by Navarro, Frenk & White. The predicted core radii are aρ = 0.20 (in units of the radius where the mean interior density is 200 times the critical density) for an Ω = 0.2 open CDM model, or aρ = 0.26 for a flat Ω = 0.2 model, with little dependence on other cosmological parameters for simulations normalized to the observed cluster abundance. The dynamically derived local mass-to-light ratio, which has little radial variation, converts the observed light profile to a mass profile. We find that the scale radius of the mass distribution, 0.20 ≤ aρ ≤ 0.30 (depending on modeling details, with a 95% confidence range of 0.12 − 0.50), is completely consistent with the predicted values. Moreover, the profiles and total masses of the clusters as individuals can be acceptably predicted from the cluster RMS line-of-sight velocity dispersion alone. This is strong support of the hierarchical clustering theory for the formation of galaxy clusters in a cool, collisionless, dark matter dominated universe. Subject headings: galaxies: clusters, cosmology: large-scale structure of universe Visiting Astronomer, Canada–France–Hawaii Telescope, which is operated by the National Research Council of Canada, le Centre National de Recherche Scientifique, and the University of Hawaii. Department of Astronomy, University of Toronto, Toronto ON, M5S 3H8 Canada Center for Astrophysics & Space Astronomy, University of Colorado, CO 80309, USA National Research Council of Canada, Herzberg Institute of Astrophysics, Dominion Astrophysical Observatory, 5071 West Saanich Road, Victoria, BC, V8X 4M6, Canada Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK Department of Physics & Astronomy, University of Victoria, Victoria, BC, V8W 3P6, Canada Department of Physics & Astronomy, University of California, Irvine, CA 92717, USA