Gravitational Lensing of the Sloan Digital Sky Survey High‐Redshift Quasars

Abstract

We predict the effects of gravitational lensing on the color-selected flux-limited samples of z(s) similar to 4.3 and zs e 5 : 8 quasars, recently published by the Sloan Digital Sky Survey (SDSS). Our main findings are the following: ( 1) The lensing probability should be 1 2 orders of magnitude higher than for conventional surveys. The expected fraction of multiply imaged quasars is highly sensitive to redshift and the uncertain slope of the bright end of the luminosity function, beta(h). For beta(h) = 2.58 (3.43) we find that at z(s) similar to 4.3 and i* < 20.0 the fraction is ∼4% (13%), while at z(s) ∼ 6 and z* < 20.2 the fraction is similar to7% (30%). (2) The distribution of magnifications is heavily skewed; sources having the redshift and luminosity of the SDSS zs e 5 : 8 quasars acquire median magnifications of med(mu(obs)) similar to1.1-1.3 and mean magni cations of (mu(obs)) similar to 5-50. Estimates of the quasar luminosity density at high redshift must therefore filter out gravitationally lensed sources. ( 3) The flux in the Gunn-Peterson trough of the highest redshift (z(s) = 6.28) quasar is known to be f(lambda) < 3 x 10(-19) ergs s(-1) cm(-2) &ANGS;(-1). Should this quasar be multiply imaged, we estimate a 40% chance that light from the lens galaxy would have contaminated the same part of the quasar spectrum with a higher flux. Hence, spectroscopic studies of the epoch of reionization need to account for the possibility that a lens galaxy, which boosts the quasar flux, also contaminates the Gunn-Peterson trough. (4) Microlensing by stars should result in ∼1/3 of multiply imaged quasars in the z(s) ≳ 5.8 catalog varying by more than 0.5 mag over the next decade. The median emission-line equivalent width of multiply imaged quasars would be lowered by ∼20% with respect to the intrinsic value because of differential magni cation of the continuum and emission-line regions.