Primordial Non-Gaussianity and the NRAO VLA Sky Survey

Abstract

The NRAO VLA Sky Survey (NVSS) is the only data set that allows an accurate determination of the auto-correlation function (ACF) on angular scales of several degrees for active galactic nuclei at z sime 1. Surprisingly, the ACF is found to be positive on large scales while, in the framework of the standard hierarchical clustering scenario with Gaussian primordial perturbations, it should be negative for a redshift-independent effective halo mass of order of that found for optically selected quasars. We show that a small primordial non-Gaussianity (NG) can add sufficient power on very large scales to account for the observed NVSS ACF. The best-fit value of the parameter f NL, quantifying the amplitude of primordial NG of local type, is f NL = 62 ? 27 (1? error bar) and 25 < f NL < 117 (2? confidence level), corresponding to a detection of NG significant at the ~3? confidence level. The minimal halo mass of NVSS sources is found to be M min = 1012.47?0.26 h ?1 M ? (1?) strikingly close to that of optically selected quasars. We discuss caveats and possible physical and systematic effects that can have an impact on the results.