The AT20G view of swift/BAT selected AGN: High-frequency radio waves meet hard X-rays

Abstract

We cross-matched the 6-year Swift/Burst Alert Telescope (BAT) survey of active galactic nuclei (AGN) with the AT20G radio survey of the southern sky, which is one of the largest high-frequency radio surveys available.With these datawe investigated the possible correlation between the radio and the X-ray emission at the highest radio and X-ray frequencies.We found 37AGNwith a high probability of association (>80 per cent), among which 19 are local Seyfert galaxies (with median redshift z=0.03) and 18 blazars.We found that˜20 per cent of theAGN detected in hard X-rays are also bright radio sources at 20 GHz, but the apparent correlation between the radio and hard X-ray luminosity is completely driven by the different median redshifts of the two subgroups of AGN. When we consider only the local Seyfert sample we find no evidence of a correlation between their 20 GHz and 15-55 keV power. Therefore it appears that at high frequencies the radio-X connection, which had been previously observed at lower frequencies, disappears. The disappearance of the radio-X correlation at high radio and X-ray frequencies could be tested through Very Long Baseline Interferometry and the use of the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.