Revisiting the Completeness and the Luminosity Function in High-Redshift Low-Luminosity Quasar Surveys

Abstract

Recent studies have derived quasar luminosity functions (QLFs) at various redshifts. However, the faint side of the QLF at high redshifts is still too uncertain. An accurate estimate of the survey completeness is essential to derive an accurate QLF for use in studying the luminosity-dependent density evolution of the quasar population. Here we investigate how the luminosity dependence of quasar spectra (the Baldwin effect) and the attenuation model for the inter-galactic medium (IGM) affect the completeness estimates. For this purpose, we revisit the completeness of quasar surveys specifically at $z\sim 4-5$, using the COSMOS images observed with Subaru/Suprime-Cam. As the result, we find that the completeness estimates are sensitive to the luminosity dependence of the quasar spectrum and difference in the IGM attenuation models. At $z\sim 4$, the number density of quasars when we adopt the latest IGM model and take the luminosity dependence of spectra into account are $(3.49\pm 1.62)\times 10^{-7}$ Mpc${}^{-3}$ mag${}^{-1}$ for $-24.09<M_{1450}<-23.09$ and $(5.24\pm 2.13)\times 10^{-7}$ Mpc${}^{-3}$ mag${}^{-1}$ for $-23.09<M_{1450}<-22.09$, respectively, which are $\sim$$24$$\%$ lower than that estimated by the conventional method. On the other hand, at $z\sim 5$, a $1\sigma$ confidence upper limit of the number density at $-24.5<M_{1450}<-22.5$ in our new estimates is $\sim$$43$$\%$ higher than that estimated previously. The results suggest that the luminosity dependence of the quasar spectrum and the IGM model are important for deriving accurate number density of high-$z$ quasars. Even taking these effects into account, the inferred luminosity-dependent density evolution of quasars is consistent with the AGN down-sizing evolutionary picture.

13 pages, 11 figures, accepted for publication in ApJ

References in corpus (15)

• The Cosmic Evolution Survey (COSMOS) -- Overview
• A luminous quasar at a redshift of z = 7.085
• An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• The Cosmic Evolution Survey (COSMOS): Subaru Observations of the HST COSMOS Field
• Natural Downsizing in Hierarchical Galaxy Formation
• Black hole masses and enrichment of z ~ 6 SDSS quasars
• The identification of z-dropouts in Pan-STARRS1: three quasars at 6.5<z<6.7
• Probing the Evolution of IR Properties of z~6 Quasars: Spitzer Observations
• Detailed Shape and Evolutionary Behavior of the X-ray Luminosity Function of Active Galactic Nuclei
• The Subaru high-z quasar survey: discovery of faint z~6 quasars
• Luminosity Function from dedicated SDSS-III and MMT data of quasars in 0.7<z<4.0 selected with a new approach
• High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function
• The Chandra COSMOS Legacy survey: the z>3 sample
• Anti-hierarchical evolution of the Active Galactic Nucleus space density in a hierarchical universe

Cited by in corpus (1)

• An Optically Faint Quasar Survey at z~5 in the CFHTLS Wide Field: Estimates of the Black Hole Masses and Eddington Ratios