Evolution of the quasar luminosity function over 3 < z < 5 in the cosmos survey field

D. Masters, P. Capak, M. Salvato, F. Civano, B. Mobasher, B. Siana, G. Hasinger, Christopher D Impey, T. Nagao, J. R. Trump, H. Ikeda, M. Elvis, N. Scoville

Research output: Contribution to journalArticle

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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 languageEnglish (US)
Article number169
JournalAstrophysical Journal
Volume755
Issue number2
DOIs
StatePublished - Aug 20 2012

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cosmos
quasars
field survey
luminosity
x rays
pollutant
active galactic nuclei
contaminants
photometry

Keywords

  • cosmology: observations
  • galaxies: luminosity function, mass function
  • Galaxy: evolution
  • quasars: general

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Masters, D., Capak, P., Salvato, M., Civano, F., Mobasher, B., Siana, B., ... Scoville, N. (2012). Evolution of the quasar luminosity function over 3 < z < 5 in the cosmos survey field. Astrophysical Journal, 755(2), [169]. https://doi.org/10.1088/0004-637X/755/2/169

Evolution of the quasar luminosity function over 3 < z < 5 in the cosmos survey field. / Masters, D.; Capak, P.; Salvato, M.; Civano, F.; Mobasher, B.; Siana, B.; Hasinger, G.; Impey, Christopher D; Nagao, T.; Trump, J. R.; Ikeda, H.; Elvis, M.; Scoville, N.

In: Astrophysical Journal, Vol. 755, No. 2, 169, 20.08.2012.

Research output: Contribution to journalArticle

Masters, D, Capak, P, Salvato, M, Civano, F, Mobasher, B, Siana, B, Hasinger, G, Impey, CD, Nagao, T, Trump, JR, Ikeda, H, Elvis, M & Scoville, N 2012, 'Evolution of the quasar luminosity function over 3 < z < 5 in the cosmos survey field', Astrophysical Journal, vol. 755, no. 2, 169. https://doi.org/10.1088/0004-637X/755/2/169
Masters, D. ; Capak, P. ; Salvato, M. ; Civano, F. ; Mobasher, B. ; Siana, B. ; Hasinger, G. ; Impey, Christopher D ; Nagao, T. ; Trump, J. R. ; Ikeda, H. ; Elvis, M. ; Scoville, N. / Evolution of the quasar luminosity function over 3 < z < 5 in the cosmos survey field. In: Astrophysical Journal. 2012 ; Vol. 755, No. 2.
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