Stellar and Total Baryon Mass Fractions in Groups and Clusters since Redshift

We investigate if the discrepancy between estimates of the total baryon mass fraction obtained from observations of the cosmic microwave background (CMB) and of galaxy groups/clusters persists when a large sample of groups is considered. To this purpose, 91 candidate X-ray groups/poor clusters at redshift 0.1 ≤ z ≤ 1 are selected from the COSMOS 2 deg survey, based only on their X–ray luminosity and extent. This sample is complemented by 27 nearby clusters for which robust analogous determinations of the total and stellar mass inside R500 are available. The total sample of 118 groups and clusters with z ≤ 1 spans a range in M500 of ∼ 10–10 M⊙. We find that the stellar mass fraction enclosed in galaxies at R500 decreases with increasing total mass as M −0.37±0.04 500 , independent of redshift. Estimating the total gas mass fraction from a recently derived, high quality scaling relation, the total baryon mass fraction (f stars+gas 500 = f stars 500 + f gas 500) is found to increase by ∼ 25% when M500 increases from 〈M〉 = 5× 10 M⊙ to 〈M〉 = 7 × 10 M⊙. After consideration of a plausible contribution due to intra–cluster light (16% of the total stellar mass), and gas depletion through the hierarchical assembly process (10% of the gas mass), the estimated values of the total baryon mass fraction are still lower than the latest CMB measure of the same quantity (WMAP5), at a significance level of 3.7σ for groups of 〈M〉 = 5 × 10 M⊙. The discrepancy decreases towards higher total masses, such that it is 1σ at 〈M〉 = 7 × 10 M⊙. We discuss this result in terms of non–gravitational processes such as feedback and filamentary heating. Subject headings: galaxies: clusters: general — galaxies: stellar content — cosmological parameters — cosmology: observations — X-rays: galaxies: clusters – diffuse radiation ⋆ Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA; also based on data collected at: the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc, under NASA contract NAS 5-26555; the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the European Southern Observatory, Chile, under Large Program 175.A-0839; and the Canada-France-Hawaii Telescope operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii. 1 Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse, Garching bei München D-85748, Germany 2 University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250. 3 INAF-Osservatorio Astronomico di Brera, Via Bianchi 46, I23807 Merate (LC), Italy 4 Spitzer Science Center, 314-6 Caltech, Pasadena, CA 91125 5 Harvard-Smithsonian Ctr. for Astrophysics (USA) 6 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822,USA 7 LBNL & Berkeley Center for Cosmological Physics, University of California, Berkeley, CA 94720, USA 8 Institute of Astronomy, Department of Physics, Eidgenssische Technische Hochschule, ETH Zurich, CH-8093, Switzerland 9 Institut d’Astrophysique de Paris, UMR 7095 CNRS, Universit Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France 10 Astronomical Institute, Graduate School of Science, Tohoku University, Aramaki, Aoba, Sendai 980-8578, Japan. 11 Physics Department, Graduate School of Science and Engineering, Ehime University, 2–5 Bunkyo–cho, Matsuyama 790–8577, Japan. 12 Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan 13 AIM Unité Mixte de Recherche CEA CNRS Université Paris VII UMR n158 14 California Institute of Technology, MC 105-24, 1200 East Cal