The 2dF QSO Redshift Survey - IX. A measurement of the luminosity dependence of QSO clustering

In this paper we present a clustering analysis of quasi-stellar objects (QSOs) as a function of luminosity over the redshift range z= 0.3-2.9. We use a sample of 10566QSOs taken from the preliminary data release catalogue of the 2dF QSO Redshift Survey (2QZ). We analyse QSO clustering as a function of apparent magnitude. The strong luminosity evolution of QSOs means that this is approximately equivalent to analysing the data as a function of absolute magnitude relative to M* over the redshift range that the 2QZ probes. Over the relatively narrow range in apparent magnitude of the 2QZ we find no significant (>2σ) variation in the strength of clustering, however, there is marginal evidence for QSOs with brighter apparent magnitudes having a stronger clustering amplitude. QSOs with 18.25 < b_J<= 19.80 show a correlation scalelength s₀= 5.50 +/- 0.79h^-1 Mpc in an Einstein-de Sitter (EdS) universe and s₀= 8.37 +/- 1.17h^-1 Mpc in a universe with Ω₀= 0.3 and λ₀= 0.7 (Λ), while the best-fitting values for the full magnitude interval (18.25 < b_J<= 20.85) over the same spatial scales are s₀= 4.29^+0.30_-0.29h^-1 Mpc (EdS) and s₀= 6.35^+0.45_-0.44h^-1 Mpc (Λ). We can therefore determine that the bias of the brightest subsample is a factor 1.22 +/- 0.15 (EdS) or 1.24 +/- 0.15 (Λ) larger than that of the full data set. An increase in clustering with luminosity, if confirmed, would be in qualitative agreement with models in which the luminosity of a QSO is correlated to the mass of the dark halo in which it resides, implying that the mass of the host plays at least some part in determining the formation of a QSO and evolution. These models predict that the clustering in brighter QSO data sets, such as the Sloan Digital Sky Survey QSO sample or the bright extension of the 2QZ, should show a higher clustering amplitude than the 2QZ.