Obscured Accretion over Cosmic Time

Details Obscured Accretion over Cosmic Time Obscured Accretion over Cosmic Time

Feb 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010head...11.3503u&link_type=abstract

American Astronomical Society, HEAD meeting #11, #35.03; Bulletin of the American Astronomical Society, Vol. 41, p.715

Astronomy and Astrophysics

Astronomy

Scientific paper

The X-ray "background” spectrum provides strong evidence that most cosmic accretion onto supermassive black holes is obscured but it does not constrain the number density of heavily obscured AGN due to parameter degeneracies. To determine the amount of heavily obscured accretion onto supermassive black holes as a function of cosmic time instead requires hard X-ray surveys plus mid- to far-infrared observations. In the local Universe, we can measure the local number density of heavily obscured active galactic nuclei (AGNs) with Swift and INTEGRAL. In the 3 Msec Ultra-Deep INTEGRAL Survey, we detect 15 X-ray sources at 5.5 sigma or better, including the well-known Compton-thick AGN, NGC 1068. These hard X-ray sources can all be identified with local bright galaxies, seven of which were not previously known X-ray sources. Absent strong evolution, transmission-dominated Compton-thick AGN like NGC 1068 contribute <10% to the cosmic X-ray "background,” and they also account for <10% of the total black hole mass accreted. The local space density of CT AGN is at present a lower limit, however, since detection of reflection-dominated CT AGN requires more sensitive hard X-ray experiments like NuSTAR and EXIST. Furthermore, heavily obscured AGN appear to evolve strongly from z 0 to z 3, more so than less obscured AGN. Taking this evolution fully into account, we still find good agreement between the radiation emitted by accreting black holes - including hard X-rays - and the local integrated black hole mass density, for an accretion efficiency of 10%.
This work was supported by NASA grants NNG05GM79G and NNX08AE15G and NSF grant 0407295.

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