The Cosmological History of Accretion onto Dark Halos and Supermassive Black Holes.pdf

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The Cosmological History of Accretion onto Dark Halos and Supermassive Black Holes.pdf

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The Cosmological History of Accretion onto Dark Halos and Supermassive Black Holes

a r X i v : a s t r o - p h / 0 6 0 8 2 0 2 v 2 1 0 A u g 2 0 0 6 Astronomy Astrophysics manuscript no. AccretionHistory c? ESO 2008 February 5, 2008 The Cosmological History of Accretion onto Dark Halos and Supermassive Black Holes L. Miller 1 , W. J. Percival 2,3 , S. M. Croom 4 , and A. Babic? 1 1 Dept. of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, U.K. 2 Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, U.K. 3 Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 2EG, U.K. 4 Anglo-Australian Observatory, PO Box 296, Epping, NSW 2121, Australia. Received / Accepted ABSTRACT Aims. We investigate the cosmological growth of dark halos and follow the consequences of coeval growth for the accretion history of associated supermassive black holes. Methods. The Press-Schechter approximation is used to obtain an analytic expression for the mean rate of growth of dark matter halos. Dark halo accretion rates are compared with numerical work and the consequences for understanding AGN evolution are described. Results. The mean accretion rate onto dark matter halos is shown to have a simple analytic form that agrees with previous numerical work and that may easily be calculated for a wide range of halo mass, redshift and cosmological parameters. The result offers a significant improvement over published fitting formulae deduced from merger trees. We then consider the growth of associated supermassive black holes, and make a basic test of the simple hypothesis of “Pure Coeval Evolution” (PCE) in which, on average, black hole growth tracks dark halo growth. We demonstrate that both the absolute value of the integrated AGN bolometric luminosity density and its cosmological evolution derived from hard X-ray surveys are well-reproduced by PCE. Excellent agreement is found at z ～ 0.5, although the observed luminosity density drops by a factor 2 compared with PCE by z = 0: b