The Density Profiles of Massive, Relaxed Galaxy Clusters: I. The Total Density Over 3 Decades in RadiusReport as inadecuate

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1 CALTECH - California Institute of Technology 2 Physics Department, UCSB 3 Department of Astronomy 4 CRAL - Centre de Recherche Astrophysique de Lyon 5 LAM - Laboratoire d-Astrophysique de Marseille

Abstract : Clusters of galaxies are excellent locations to probe the distribution of baryons and dark matter over a wide range of scales. We study a sample of 7 massive, relaxed galaxy clusters with centrally-located brightest cluster galaxies BCGs at z=0.2-0.3. Using the observational tools of strong and weak gravitational lensing, combined with resolved stellar kinematics within the BCG, we measure the total radial density profile, comprising both dark and baryonic matter, over scales of \sim3-3000 kpc. Lensing-derived mass profiles typically agree with independent X-ray estimates within \sim15%, suggesting that departures from hydrostatic equilibrium are small and that the clusters in our sample except A383 are not strongly elongated along the line of sight. The inner logarithmic slope gamma tot of the total density profile measured over r-r200=0.003-0.03, where rho tot \sim r^-gamma tot, is found to be nearly universal, with a mean = 1.16 +- 0.05 random +0.05-0.07 systematic and an intrinsic scatter of < 0.13 68% confidence. This is further supported by the very homogeneous shape of the observed velocity dispersion profiles, obtained via Keck spectroscopy, which are mutually consistent after a simple scaling. Remarkably, this slope agrees closely with numerical simulations that contain only dark matter, despite the significant contribution of stellar mass on the scales we probe. The Navarro-Frenk-White profile characteristic of collisionless cold dark matter is a better description of the total mass density at radii \gtrsim 5-10 kpc than that of dark matter alone. Hydrodynamical simulations that include baryons, cooling, and feedback currently provide a poorer match. We discuss the significance of our findings for understanding the assembly of BCGs and cluster cores, particularly the influence of baryons on the inner dark matter halo. abridged

Keywords : Cosmology and Extragalactic Astrophysics Astrophysics

Author: Andrew B. Newman - Tommaso Treu - Richard S. Ellis - David J. Sand - Carlo Nipoti - Johan Richard - Eric Jullo -



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