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For refcode 2002ApJ...565L...5B:
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2002ApJ...565L...5B Antibias in Clusters: The Dependence of the Mass-to-Light Ratio on Cluster Temperature Neta A. Bahcall and Julia M. Comerford Princeton University Observatory, Peyton Hall, Ivy Lane, Princeton, NJ 08544-1001; neta@astro.princeton.edu, comerfrd@astro.princeton.edu Received 2001 September 19; accepted 2001 December 17; published 2002 January 3 ABSTRACT We show that the observed mass-to-light (M/L) ratio of galaxy clusters increases with cluster temperature as expected from cosmological simulations. Contrary to previous observational suggestions, we find a mild but robust increase of M/L from poor (T ~ 1-2 keV) to rich (T ~ 12 keV) clusters; over this range, the mean M/L_V_ increases by a factor of about 2. The best-fit relation satisfies M/L_V_ = (170 +/- 30)T_keV_^0.3+/-0.1^ h at z = 0, with a large scatter. This trend confirms predictions from cosmological simulations that show that the richest clusters are antibiased, with a higher ratio of mass per unit light than average. The antibias increases with cluster temperature. The effect is caused by the relatively older age of the high-density clusters, where light has declined more significantly than average since their earlier formation time. Combining the current observations with simulations, we find a global value of M/L_V_ = 240 +/- 50 h and a corresponding mass density of the universe of {OMEGA}_m_ = 0.17 +/- 0.05. Subject headings: cosmology: observations - cosmology: theory - dark matter - galaxies: clusters: general - large-scale structure of universe
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