Open AccessThe unresolved hard X‐ray background: the missing source population implied by the Chandra and XMM–Newton deep fields
Author(s) -
Worsley M. A.,
Fabian A. C.,
Bauer F. E.,
Alexander D. M.,
Hasinger G.,
Mateos S.,
Brunner H.,
Brandt W. N.,
Schneider D. P.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.08731.x
Subject(s) - physics , astrophysics , hubble deep field , chandra deep field south , redshift , x ray background , active galactic nucleus , population , astronomy , source counts , galaxy , medicine , environmental health
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 (CDF‐N) and the 1‐Ms Chandra Deep Field South (CDF‐S). The XMM–Newton work showed the resolved fraction of the X‐ray background (XRB) 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 XRB component has a spectral shape that is consistent with a population of highly obscured active galactic nuclei (AGN) at redshifts ∼0.5–1.5 and with absorption column densities of ∼10 23 –10 24 cm −2 .