On the detectability of distant Compton-thick obscured quasars |
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| Authors: | AC Fabian RJ Wilman CS Crawford |
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| Institution: | 1Institute of Astronomy, Madingley Road, Cambridge CB3 0HA;2Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, the Netherlands |
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| Abstract: | Chandra and XMM–Newton have resolved the  X-ray background (XRB) into point sources. Many of the fainter sources are obscured active galactic nuclei (AGN) with column densities in the range of  , some of which have quasar-like luminosities. According to obscuration models, the XRB above 8 keV is dominated by emission from Compton-thick AGN, with column densities exceeding  . Here, we consider whether Compton-thick quasars are detectable by Chandra and XMM–Newton by their direct (i.e. not scattered) X-ray emission. Detectability is optimized if the objects individually have a high luminosity and high redshift, so that the direct emission has a significant flux in the observed band. Using a simple galaxy formation model incorporating accreting black holes, in which quasars build most of their mass in a Compton-thick manner before expelling the obscuring matter, we predict that moderately deep 100-ks Chandra and XMM–Newton exposures may contain a handful of detectable Compton-thick quasars. Deep Ms or more Chandra images should contain  distant, optically faint, Compton-thick sources. In passing we show that radiation pressure can be as effective in expelling the obscuring gas as quasars winds, and yields a black hole mass proportional to the velocity dispersion of the host bulge to the fourth power. |
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| Keywords: | galaxies: active quasars: general galaxies: Seyfert infrared: galaxies X-rays: general |
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