Cosmic evolution of quasar clustering: implications for the host haloes

Abstract

We present detailed clustering measurements from the 2dF Quasi-Stellar Object Redshift Survey (2QZ) in the redshift range 0.8 < z < 2.1. Using a flux-limited sample of ∼14 000 objects with effective redshift z eff = 1.47, we estimate the quasar projected correlation function for separations 1 < r/ h −1 Mpc < 20. We find that the two-point correlation function in real space is well approximated by a power law with slope γ = 1.5 ± 0.2 and comoving correlation length r 0 = 4.8 +0.9 h −1 Mpc. Splitting the sample into three subsets based on redshift, we find evidence for an increase of the clustering amplitude with look-back time. For a fixed γ ,e v olution of r0 is detected at the 3.6σ confidence level. The ratio between the quasar correlation function and the mass autocorrelation function (derived adopting the concordance cosmological model) is found to be scale-independent. For a linear mass-clustering amplitude σ 8 = 0.8, the ‘bias parameter’ decreases from b � 3.9 at z eff = 1.89 to b � 1.8 at z eff = 1.06. From the observed abundance and clustering, we infer how quasars populate dark matter