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|Title:||Evidence for a large fraction of compton-thick quasars at high redshift|
Bonfield, D. G.
|Publisher:||Royal Astronomical Society (RAS)|
|Citation:||Monthly Notices of the Royal Astronomical Society: LETTERS, 2007, 379 (1)|
|Abstract:||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-μm 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.|
|Rights:||This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2007 the authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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