Clustering of low-redshift (z ≤ 2.2) quasars from the sloan digital sky survey

We present measurements of the Quasar Two-Point Correlation Function, Ξ_Q, over the redshift range 0.3 ≤ z ≤ 2.2 based upon a homogeneous sample of 38,208 quasars with spectroscopic redshifts from the Data Release 5 Quasar Catalogue. Over this redshift range, we find that the redshift-space correlation function, Ξ(s), is well-fit by a single power-law, with s₀ = 5.95 ±0.45 h^-1 Mpc and γ_s = 1.16_-0.16^+0.11 when fit over 1.0 ≤ s ≤ 25.0 h^-1 Mpc. Dividing the sample into redshift slices, we find no evidence for evolution of quasar clustering, with the correlation length staying roughly constant at s₀ ∼ 6 - 7 h^-1 Mpc at z ≲ 2.2. Comparing our clustering measurements to those reported for X-ray selected AGN at z ∼ 0.5 -1, we find reasonable agreement in some cases but significantly lower correlation lengths in others. Assuming a standard ACDM cosmology, we find the linear bias evolves from b ∼ 1.4 at z = 0.5 to b ∼ 3 at z = 2.2, with b(z = 1.27) = 2.06 ± 0.03 for the full sample. We compare our data to analytical models and infer that quasars inhabit dark matter haloes of constant mass M_halo ∼ 1 -2×10 ¹²h^-1M_⊙ from redshifts z ∼ 2.5 (the peak of quasar activity) to z ∼ 0. The measured evolution of the clustering amplitude is in reasonable agreement with recent theoretical models, although measurements to fainter limits will be needed to distinguish different scenarios for quasar feeding and black hole growth.