The NRAO VLA Sky Survey ( NVSS ) is the only dataset that allows an accurate determination of the auto-correlation function ( ACF ) on angular scales of several degrees for active galactic nuclei at z \simeq 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 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 non-Gaussianity of local type , is f _ { NL } = 62 \pm 27 ( 1 \sigma error bar ) and 25 < f _ { NL } < 117 ( 2 \sigma confidence level ) , corresponding to a detection of non-Gaussianity significant at the \sim 3 \sigma confidence level .
The minimal halo mass of NVSS sources is found to be M _ { min } = 10 ^ { 12.47 \pm 0.26 } h ^ { -1 } M _ { \odot } ( 1 \sigma ) strikingly close to that of optically selected quasars .
We discuss caveats and possible physical and systematic effects that can impact on the results .