Quasar Populations in a Cosmological Constant Dominated Flat Universe

Abstract

Most physical properties derived for quasars, as single entities or as a population, depend upon the cosmology assumed. In this paper, we calculate the quasar luminosity function and some related quantities for a flat universe dominated by a cosmological constant $Λ$ ($Λ=0.9, Ω=0.1$) and compare them with those deduced for a flat universe with zero cosmological constant ($Λ=0,Ω=1$). We use the AAT quasar survey data (Boyle et al. 1990) as input in both cases. The data are fit well by a pure luminosity evolution model for both the cosmologies, but with different evolutionary parameters. From the luminosity function, we predict (extrapolate) a greater number of quasars at faint apparent magnitudes (twice the number at B=24, $z < 2.2$) for the $Λ$ dominated universe. This population of faint quasars at high redshift would result in a higher incidence of gravitational lensing. The total luminosity of the quasar population and the total mass tied up in black hole remnants of quasars is not sensitive to the cosmology. However, for a $Λ$ cosmology this mass is tied up in fewer but more massive black holes.