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A population of high-redshift type 2 quasars – I. Selection criteria and optical spectra

Martínez-Sansigre, Alejo and Rawlings, Steve and Lacy, Mark and Fadda, Dario and Jarvis, Matt J. and Marleau, Francine R. and Simpson, Chris and Willott, Chris J. (2006) A population of high-redshift type 2 quasars – I. Selection criteria and optical spectra. Monthly Notices of the Royal Astronomical Society, 370 (3). pp. 1479-1498. ISSN 0035-8711. doi:10.1111/j.1365-2966.2006.10563.x.

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We discuss the relative merits of mid-infrared and X-ray selection of type 2 quasars. We describe the mid-infrared, near-infrared and radio selection criteria used to find a population of redshift z∼ 2 type 2 quasars which we previously argued suggests that most supermassive black hole growth in the Universe is obscured. We present the optical spectra obtained from the William Herschel Telescope, and we compare the narrow emission-line luminosity, radio luminosity and maximum size of jets to those of objects from radio-selected samples. This analysis suggests that these are genuine radio-quiet type 2 quasars, albeit the radio-bright end of this population. We also discuss the possibility of two different types of quasar obscuration, which could explain how the ∼2–3:1 ratio of type 2 to type 1 quasars preferred by modelling our population can be reconciled with the ∼1:1 ratio predicted by unified schemes.

Item Type:Article
Related URLs:
URLURL TypeDescription
Lacy, Mark0000-0002-3032-1783
Fadda, Dario0000-0002-3698-7076
Jarvis, Matt J.0000-0001-7039-9078
Willott, Chris J.0000-0002-4201-7367
Additional Information:© 2006 The Authors. Journal compilation © 2006 RAS. Accepted 2006 May 15. Received 2006 May 15; in original form 2006 January 20. We would like to warmly thank Richard Wilman for access to his absorbed X-ray spectra and for useful comments, the anonymous referee for valuable suggestions, and Caroline van Breukelen for help with the overlays. AMS would like to thank the Council of the European Union for support; SR and CS would like to thank the UK PPARC for a Senior Research Fellowship and an Advanced Fellowship, respectively. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology. The William Herschel Telescope (WHT) is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatory del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
Funding AgencyGrant Number
European Research Council (ERC)UNSPECIFIED
Particle Physics and Astronomy Research Council (PPARC)UNSPECIFIED
Subject Keywords:active galaxies; galactic nuclei; quasars
Issue or Number:3
Record Number:CaltechAUTHORS:MARmnras06
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11228
Deposited By: Tony Diaz
Deposited On:06 Aug 2008 04:31
Last Modified:08 Nov 2021 21:34

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