A population of high-redshift type 2 quasars – I. Selection criteria and optical spectra |
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| Authors: | Alejo Martínez-Sansigre Steve Rawlings Mark Lacy Dario Fadda Matt J Jarvis Francine R Marleau Chris Simpson Chris J Willott |
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| Institution: | Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH;Spitzer Science Center, California Institute of Technology, MS220-6, 1200 E. California Boulevard, Pasadena, CA 91125, USA;Department of Physics, University of Durham, South Road, Durham DH1 3LE;Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD;Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Rd, Victoria, B.C. V9E 2E7, Canada |
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| Abstract: | 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. |
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| Keywords: | galaxies: active galaxies: nuclei quasars: general |
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