QSO clustering - I. Optical surveys in the redshift range 0.3 < z < 2.2

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Abstract
We present QSO clustering results from ≈ 700 QSOs detected in three surveys, including the Durham/AAT UVX Survey. We have made a 4σ detection of QSO clustering at scales of < 10 h–1 Mpc (q0 = 0.5), stronger than expected on the basis of models of the evolution of the galaxy correlation function where the clustering is assumed to be stable in proper coordinates. A model in which QSOs randomly sample a galaxy distribution with present-day clustering coherence length, r0 ≈ 6 h–1 Mpc, and which is fixed in comoving coordinates, is strongly suggested by the data; a stable-clustering, high-amplitude (r0 ≈ 11 h–1 Mpc) model can be excluded when the low-redshift Seyfert clustering results of Georgantopoulos & Shanks (Paper II) are considered. The conclusion that ultraviolet-excess (UVX) QSOs randomly sample the underlying galaxy distribution is also given strong support from the observation by Ellingson, Yee & Green that the clustering environment of z ≈ 0.6 radio-quiet QSOs is no different from that of average galaxies. Our results therefore suggest that a comoving model may also describe the evolution of galaxy clustering out to z = 2.2; such a model is consistent with biased models of galaxy clustering with either q0 = 0.01 or q0 = 0.5. We have also tentatively detected, at a lower level of significance ( ≈ 2 σ), anticorrelation at the ξ ≈ –0.1 level in the range 40 < r < 100 h–1 Mpc in the q0 = 0.5 QSO correlation function. Anticorrelation is expected in models where the power-law spectral index, n, of the primordial mass spectrum has a value ≥ 1. No other features are detectable at the ± 0.05 level in ξ at any scale in the range 10 < r < 1000 h–1 Mpc. Finally, we show that the spatial position of features in the QSO correlation function is very sensitive to the cosmological model. In particular, we find that, in a model with zero spatial curvature, Ʌ ≠ 0 and Ω0 < 0.03, the QSO clustering extends up to a comoving scale of ≈ 40 h–1 Mpc, and we suggest that, at the 3σ level, it is difficult to reconcile this Ʌ ≠ 0 result with the known correlation functions of galaxies and Seyferts at low redshift.

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