Most hard X-ray selected quasars in Chandra Deep Fields are obscured

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dc.creatorWang, J. X.
dc.creatorJiang, P.
dc.creatorZheng, Z. Y.
dc.creatorTozzi, P.
dc.creatorNorman, C.
dc.creatorGiacconi, R.
dc.creatorGilli, R.
dc.creatorHasinger, G.
dc.creatorKewley, L.
dc.creatorMainieri, V.
dc.creatorNonino, M.
dc.creatorRosati, P.
dc.creatorStreblyanska, A.
dc.creatorSzokoly, G.
dc.creatorZirm, A.
dc.creatorZheng, W.
dc.date2006-11-08
dc.date.accessioned2026-07-07T10:24:13Z
dc.date.available2026-07-07T10:24:13Z
dc.descriptionMeasuring the population of obscured quasars is one of the key issues to understand the evolution of active galactic nuclei (AGNs). With a redshift completeness of 99%, the X-ray sources detected in Chandra Deep Field South (CDF-S) provide the best sample for this issue. In this letter we study the population of obscured quasars in CDF-S by choosing the 4 -- 7 keV selected sample, which is less biased by the intrinsic X-ray absorption. The 4 -- 7 keV band selected samples also filter out most of the X-ray faint sources with too few counts, for which the measurements of N_H and L_X have very large uncertainties. Simply adopting the best-fit L_2-10keV and N_H, we find 71% (20 out of 28) of the quasars (with intrinsic L_2-10keV > 10^44 erg/s) are obscured with N_H > 10^22 cm^-2. Taking account of the uncertainties in the measurements of both N_H and L_X, conservative lower and upper limits of the fraction are 54% (13 out 24) and 84% (31 out 37). In Chandra Deep Field North, the number is 29%, however, this is mainly due to the redshift incompleteness. We estimate a fraction of ~ 50% - 63% after correcting the redshift incompleteness with a straightforward approach. Our results robustly confirm the existence of a large population of obscured quasars.
dc.description18 pages, including 6 figures and 1 table, ApJ accepted (submitted on Apr. 10)
dc.identifierhttps://arxiv.org/abs/astro-ph/0611251
dc.identifierhttp://arxiv.org/abs/astro-ph/0611251
dc.identifierAstrophys.J.657:95-101,2007
dc.identifierdoi:10.1086/510766
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/176105
dc.subjectAstrophysics
dc.titleMost hard X-ray selected quasars in Chandra Deep Fields are obscured
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