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The unresolved hard X-ray background: the missing source population implied by the Chandra and XMM-Newton deep fields

M. A. Worsley·A. C. Fabian·F. E. Bauer·D. M. Alexander·G. Hasinger·S. Mateos·H. Brunner·W. N. Brandt·D. P. Schneider
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Abstract

We extend our earlier work on X-ray source stacking in the deep XMM-Newton observation of the Lockman Hole, to the 2 Ms Chandra Deep Field North and the 1 Ms Chandra Deep Field South. The XMM-Newton work showed the resolved fraction of the X-ray background to be ~80-100 per cent at <2 keV but this decreased to only ~50 per cent above ~8 keV. The CDF-N and CDF-S probe deeper, and are able to fill-in some of the missing fraction in the 4-6 keV range, but the resolved fraction in the 6-8 keV band remains only ~60 per cent, confirming the trend seen with XMM-Newton. The missing X-ray background component has a spectral shape that is consistent with a population of highly obscured AGN at redshifts \~0.5-1.5 and with absorption column densities of ~10^23 - 10^24 cm^-2.

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M. A. Worsley, A. C. Fabian, F. E. Bauer, D. M. Alexander, G. Hasinger, S. Mateos, H. Brunner, W. N. Brandt, D. P. Schneider. 2004-12-12. The unresolved hard X-ray background: the missing source population implied by the Chandra and XMM-Newton deep fields. https://doi.org/10.1111/j.1365-2966.2005.08731.x%2Fabs%2F

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