Paper detail

The role of galaxy mass on AGN emission: a view from the VANDELS survey

We present a comparative analysis of the properties of AGN emitting at radio and X-ray wavelengths. The study is performed on 907 X-ray AGN and 100 radio AGN selected on the CDFS and UDS fields and makes use of new and ancillary data available to the VANDELS collaboration. Our results indicate that the mass of the host galaxy is a fundamental quantity which determines the level of AGN activity at the various wavelengths. Indeed large stellar masses are found to be connected with AGN radio emission, as virtually all radio-active AGN reside within galaxies of M*>10^{10} Msun. Large stellar masses also seem to favour AGN activity in the X-ray, even though X-ray AGN present a mass distribution which is more spread out and with a non-negligible tail at M*<10^{9} Msun. Stellar mass alone is also observed to play a fundamental role in simultaneous radio and X-ray emission: the percentage of AGN active at both wavelengths increases from around 1% of all X-ray AGN residing within hosts of M*<10^{11} Msun to about 13% in more massive galaxies. In the case of radio-selected AGN, such a percentage moves from about 15% to about 45% (but up to 80% in the deepest fields). Neither cosmic epoch, nor radio luminosity, X-ray luminosity, Eddington ratio or star-formation rate of the hosts are found to be connected to an enhanced probability for joint radio+X-ray emission of AGN origin. Furthermore, only a loose relation is observed between X-ray and radio luminosity in those AGN which are simultaneously active at both frequencies.