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S. M. Croom, B. J. Boyle (AAO), T. Shanks (University of Durham), R.J. Smith (Liverpool John Moores University), L. Miller, N. S. Loaring (University of Oxford)
We present clustering results from the 2dF QSO Redshift Survey (2QZ), which upon completion will contain over 25000 QSOs. The current data set consists of over 15000 QSOs in the redshift range z=0.3-2.9, so is already by far the largest QSO sample in existence.
We measure the two-point redshift-space correlation function of the QSOs in the 2QZ. This is shown to be a power law for the first time. The power law extends to 35h-1Mpc in an Einstein-de-Sitter (EdS) universe. The slope and amplitude of the power law, at a mean redshift of z=1.5, is similar to that of local (z~.05) galaxies. For a power law of the form \xi(s)=(s/s0)-\gamma we find s0=4.23+0.33-0.38h-1Mpc and \gamma=1.50+0.11-0.10 (EdS). A strong cosmological constant term increases the amplitude of clustering, so that for \lambda0=0.7 and \Omega0=0.3 we find s0=5.90+0.52-0.66h-1Mpc and \gamma=1.45+0.11-0.09, and the power law extends to ~0h-1Mpc.
We also measure the clustering of QSOs as a function of redshift. For an EdS universe QSO clustering is constant (in comoving coordinates) over our entire redshift range. QSOs thus have similar clustering properties to local galaxies at all redshifts that we sample. In a cosmological constant dominated universe there is a marginal increase in clustering with increasing redshift. Although QSO clustering is measured on large scales where linear theory should apply, QSOs do not follow the linear theory predictions for growth via gravitational instability. Thus a redshift dependent QSO bias is required. Simple models based on the Press-Schechter formalism are consistent with QSO clustering for minimum halo masses of ~1012M\odot (EdS) or ~1013M\odot (\lambda=0.7, \Omega0=0.3).