The large-scale clustering of radio galaxies

Abstract

We use an all-sky sample of radio galaxies at redshifts z ≲ 0.1 to study clustering in the Universe on scales up to several hundred Mpc. The two-point correlation function for these galaxies is consistent with their high optical luminosity and location in moderately rich environments: ξ(r)≃(r/11 h-1 Mpc)-1.8, where h ≡ H0/100 km s-1 Mpc-1. We discuss direct methods for obtaining the power spectrum of the density field traced by the radio galaxies, taking into account the selection function of the sample. The results of the power-spectrum analysis indicate that the distribution of radio galaxies is more uniform on very large scales than would be predicted from an extrapolation of the power-law clustering found on small scales. There is a break to an effective spectral index n ≳ - 0.5 for wavelengths λ ≳ 200 h-1 Mpc. The variance in δ N/N, σ2, is about 0.3 for wavelengths 80 <200 h-1 Mpc, and there is no concentration towards the supergalactic plane for z ≳ 0.02. We thus do not confirm suggestions made by Broadhurst et al. and by Tully of strong clustering on scales of ≳ 100Mpc.