Abstract
We investigate the high-redshift quasar luminosity function (QLF) down to an apparent magnitude of I AB = 25 in the Cosmic Evolution Survey (COSMOS). Careful analysis of the extensive COSMOS photometry and imaging data allows us to identify and remove stellar and low-redshift contaminants, enabling a selection that is nearly complete for type-1 quasars at the redshifts of interest. We find 155 likely quasars at z > 3.1, 39 of which have prior spectroscopic confirmation. We present our sample in detail and use these confirmed and likely quasars to compute the rest-frame UV QLF in the redshift bins 3.1 < z < 3.5 and 3.5 < z < 5. The space density of faint quasars decreases by roughly a factor of four from z 3.2 to z 4, with faint-end slopes of β -1.7 at both redshifts. The decline in space density of faint optical quasars at z > 3 is similar to what has been found for more luminous optical and X-ray quasars. We compare the rest-frame UV luminosity functions found here with the X-ray luminosity function at z > 3, and find that they evolve similarly between z 3.2 and z 4; however, the different normalizations imply that roughly 75% of X-ray bright active galactic nuclei (AGNs) at z 3-4 are optically obscured. This fraction is higher than found at lower redshift and may imply that the obscured, type-2 fraction continues to increase with redshift at least to z 4. Finally, the implications of the results derived here for the contribution of quasars to cosmic reionization are discussed.
Original language | English (US) |
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Article number | 169 |
Journal | Astrophysical Journal |
Volume | 755 |
Issue number | 2 |
DOIs | |
State | Published - Aug 20 2012 |
Keywords
- Galaxy: evolution
- cosmology: observations
- galaxies: luminosity function, mass function
- quasars: general
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
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Masters, D. (Creator), Capak, P. (Creator), Salvato, M. (Creator), Civano, F. (Creator), Mobasher, B. (Creator), Siana, B. (Creator), Hasinger, G. (Creator), Impey, C. D. (Creator), Nagao, T. (Creator), Trump, J. R. (Creator), Ikeda, H. (Creator), Elvis, M. (Creator) & Scoville, N. (Creator), Centre de Donnees Strasbourg (CDS), 2017
DOI: 10.26093/cds/vizier.17550169, https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/755/169
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