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The cosmic X-ray background from scaling galactic black holes to AGN

Chris Done, durham

The stellar mass black holes in binary systems show a wide range of spectra. These peak at 100 keV with a thermal rollover only at low luminosities (the low/hard state). At higher fractions of Eddington they show spectra which are unbroken at high energies. Scaling these models up to the supermassive black holes in AGN predicts that high Eddington fraction accretion flows, which dominate redshift~2 where the quasar number counts peak, do not show the characteristic high energy rollover required to match the Cosmic X-ray background. I will discuss the implications of this for the origin of the CXB and the numbers of obscured AGN.