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High-redshift QSOs in the SWIRE Survey and the z~3 QSO luminosity function

Siana, Brian and Polletta, Maria del Carmen and Smith, Harding E. and Lonsdale, Carol J. and Gonzalez-Solares, Eduardo and Farrah, Duncan and Babbedge, Tom S. R. and Rowan-Robinson, Michael and Surace, Jason and Shupe, David and Fang, Fan and Franceschini, Alberto and Oliver, Seb (2008) High-redshift QSOs in the SWIRE Survey and the z~3 QSO luminosity function. Astrophysical Journal, 675 (1). pp. 49-70. ISSN 0004-637X. doi:10.1086/527025.

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We use a simple optical/infrared (IR) photometric selection of high-redshift QSOs that identifies a Lyman break in the optical photometry and requires a red IR color to distinguish QSOs from common interlopers. The search yields 100 z ~ 3 (U-dropout) QSO candidates with 19 < r' < 22 over 11.7 deg^2 in the ELAIS-N1 (EN1) and ELAIS-N2 (EN2) fields of the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy Survey. The z ~ 3 selection is reliable, with spectroscopic follow-up of 10 candidates confirming that they are all QSOs at 2.83 < z < 3.44. We find that our z ~ 4 (g'-dropout) sample suffers from both unreliability and incompleteness but present seven previously unidentified QSOs at 3.50 < z < 3.89. Detailed simulations show our z ~ 3 completeness to be ~80%-90% from 3.0 < z < 3.5, significantly better than the ~30%-80% completeness of the SDSS at these redshifts. The resulting luminosity function extends 2 mag fainter than SDSS and has a faint-end slope of β = − 1.42 ± 0.15, consistent with values measured at lower redshift. Therefore, we see no evidence for evolution of the faint-end slope of the QSO luminosity function. Including the SDSS QSO sample, we have now directly measured the space density of QSOs responsible for ~70% of the QSO UV luminosity density at z ~ 3. We derive a maximum rate of H I photoionization from QSOs at z ~ 3.2, Γ = 4.8 × 10^(−13) s^(−1), about half of the total rate inferred through studies of the Lyα forest. Therefore, star-forming galaxies and QSOs must contribute comparably to the photoionization of H I in the intergalactic medium at z ~ 3.

Item Type:Article
Related URLs:
URLURL TypeDescription
Siana, Brian0000-0002-4935-9511
Polletta, Maria del Carmen0000-0001-7411-5386
Lonsdale, Carol J.0000-0003-0898-406X
Farrah, Duncan0000-0003-1748-2010
Surace, Jason0000-0001-7291-0087
Shupe, David0000-0003-4401-0430
Oliver, Seb0000-0001-7862-1032
Additional Information:© 2008 The American Astronomical Society. Received 2006 April 11; accepted 2007 October 31. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work, part of the Spitzer Space Telescope Legacy Science Program, was provided by NASA through an award issued by JPL/Caltech, under NASA contract 1407. Based in part on observations obtained at the Hale Telescope, Palomar Observatory as part of a continuing collaboration between the California Institute of Technology, NASA/JPL, and Cornell University. Based in part on data made publicly available through the Isaac Newton Group’s Wide Field Camera Survey Programme. The Isaac Newton Telescope is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Canarias. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. Facilities: Spitzer( IRAC, MIPS).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:intergalactic medium; quasars: general
Issue or Number:1
Record Number:CaltechAUTHORS:20090427-091319525
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14081
Deposited By: Tony Diaz
Deposited On:07 Aug 2009 18:22
Last Modified:08 Nov 2021 22:42

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