The correlation function of radio sources

We investigate the large-scale clustering of radio sources in the Green Bankand Parkes-MIT-NRAO 4.85 GHz surveys by measuring the angular two-pointcorrelation function w(\theta). Excluding contaminated areas, the two surveystogether cover 70 per cent of the whole sky. We find both surveys to bereasonably complete above 50 mJy. On the basis of previous studies, the radiosources are galaxies and radio-loud quasars lying at redshifts up to z \sim 4,with a median redshift z \sim 1. This provides the opportunity to probelarge-scale structures in a volume far larger than that within the reach ofpresent optical and infrared surveys. We detect a clustering signal w(\theta)\approx 0.01 for \theta = 1\degr. By assuming an evolving power-law spatialcorrelation function in comoving coordinates \xi(r_c,z) = ( r_c / r_0)^{-\gamma} (1+z)^{\gamma-(3+\epsilon)}, where \gamma = 1.8, and the redshiftdistribution N(z) of the radio galaxies, we constrain the r_0--\epsilonparameter space. For `stable clustering' (\epsilon = 0), we find thecorrelation length r_0 \approx 18 Mpc/h, larger than the value for nearbynormal galaxies and comparable to the cluster-cluster correlation length.Comment: 8 pages, 7 ps figures included, LaTeX (mn,sty). Accepted by MNRA