A survey of luminous high-redshift quasars with SDSS and WISE II. the bright end of the quasar luminosity function at z ~ 5

Abstract

This is the second paper in a series on a new luminous z ~ 5 quasar survey using optical and near-infrared colors. Here we present a new determination of the bright end of the quasar luminosity function (QLF) at z ~ 5. Combined our 45 new quasars with previously known quasars that satisfy our selections, we construct the largest uniform luminous z ~ 5 quasar sample to date, with 99 quasars in the range 4.7 <= z < 5.4 and -29 < M1450 <= -26.8, within the Sloan Digital Sky Survey (SDSS) footprint. We use a modified 1/Va method including flux limit correction to derive a binned QLF, and we model the parametric QLF using maximum likelihood estimation. With the faint-end slope of the QLF fixed as alpha = -2.03 from previous deeper samples, the best fit of our QLF gives a flatter bright end slope beta = -3.58+/-0.24 and a fainter break magnitude M*1450 = -26.98+/-0.23 than previous studies at similar redshift. Combined with previous work at lower and higher redshifts, our result is consistent with a luminosity evolution and density evolution (LEDE) model. Using the best fit QLF, the contribution of quasars to the ionizing background at z ~ 5 is found to be 18% - 45% with a clumping factor C of 2 - 5. Our sample suggests an evolution of radio loud fraction with optical luminosity but no obvious evolution with redshift.

14 pages, 12 figures, Accepted by ApJ

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• Streamlined Lensed Quasar Identification in Multiband Images via Ensemble Networks
• Pure Density Evolution of the Ultraviolet Quasar Luminosity Function at $2\lesssim z\lesssim 6$
• The Infrared Medium-deep Survey. III. Survey of Luminous Quasars at 4.7 $\le$ z $\le$ 5.4
• Chandra Detection of Three X-ray Bright Quasars at z>5
• Quasar UV Luminosity Function at $3.5<z<5.0$ from SDSS Deep Imaging Data
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• Paving the Way for Euclid and JWST via Optimal Selection of High-z Quasars
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• Reality or Mirage? Observational Test and Implications for the Claimed Extremely Magnified Quasar at $z=6.3$
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• Ultra-luminous high-redshift quasars from SkyMapper -- II. New quasars and the bright end of the luminosity function