The Clustering of Radio Galaxies: Biasing and Evolution Versus Stellar Mass

We study the angular clustering of ~ 6× 10⁵ NVSS sources on scales 50 h⁻¹ Mpc in the context of the ΛCDM scenario. The analysis partially relies on the redshift distribution of 131 radio galaxies, inferred from the Hercules and CENSORS survey, and an empirical fit to the stellar to halo mass (SHM) relation. For redshifts z 0.7, the fraction of radio activity versus stellar mass evolves as f_RL~ M_*α₀+α₁ z where α₀=2.529±0.184 and α₁=1.854+0.708-0.761. The estimate on α₀ is largely driven by the results of Best et al. (2005), while the constraint on α₁ is new. We derive a biasing factor b(z=0.5)=2.093+0.164-0.109 between radio galaxies and the underlying mass.The function b(z)=0.33z²+0.85 z +1.6 fits well the redshift dependence. We also provide convenient parametric forms for the redshift dependent radio luminosity function, which are consistent with the redshift distribution and the NVSS source count versus flux.