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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 358657.0, MPI für Astronomie / Publikationen_mpia
Evidence for a large fraction of Compton-thick quasars at high redshift
Authors:Martínez-Sansigre, A.; Rawlings, S.; Bonfield, D. G.; Mateos, S.; Simpson, C.; Watson, M.; Almaini, O.; Foucaud, S.; Sekiguchi, K.; Ueda, Y.
Date of Publication (YYYY-MM-DD):2007
Title of Journal:Monthly Notices of the Royal Astronomical Society
Start Page:L6
End Page:L10
Audience:Not Specified
Abstract / Description:Using mid-infrared and radio selection criteria, we pre-select a sample of candidate high-redshift type 2 quasars in the Subaru XMM-Newton Deep Field (SXDF). To filter out starburst contaminants, we use a Bayesian method to fit the spectral energy distributions (SEDs) between 24-mum and the B-band, obtain photometric redshifts, and identify the best candidates for high-z type 2 quasars. This leaves us with 12 zphot >= 1.7 type 2 quasar candidates in an area ~0.8 deg2, of which only two have secure X-ray detections. The two detected sources have estimated column densities NH ~ 2 & 3 × 1027 m-2, i.e. heavily obscured but Compton-thin quasars. Given the large bolometric luminosities and redshifts of the undetected objects, the lack of X-ray detections suggests extreme absorbing columns NH >~ 1028 m-2 are typical. We have found evidence for a population of `Compton-thick' high-redshift type 2 quasars, at least comparable to, and probably larger than, the type 1 quasar population, although spectroscopic confirmation of their active galactic nuclei nature is important.
Free Keywords:galaxies: active ; galaxies: nuclei ; quasars: general ; X-rays: galaxies
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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