Where to look for radiatively inefficient accretion flows (and find them)

Abstract

We have studied the nuclear emission detected in high-resolution radio and optical data of carefully selected samples of low luminosity AGN (LLAGN) in the local universe. When the Eddington ratio is plotted against the nuclear ``radio-loudness'' parameter, sources divide according to their physical properties. It is thus possible to disentangle between nuclear jets and accretion disks of different radiative efficiencies. If this simple interpretation is correct, we now have a powerful tool to investigate the nature of the nuclear radiation, and identify radiatively inefficient accretion flows (RIAF) candidates. Our results show that the best chance of investigating RIAF processes in the IR-to-UV spectral region is to observe (at the resolution provided by HST) the nuclei of unobscured Seyferts of the lowest luminosity, as well as a sub-class of LINERs. In all other objects other radiation processes dominate. In a sample of 132 LLAGN we identify 8 objects in which we predict the radiation from a RIAF can be directly detected.