A link between radio loudness and X-ray/optical properties of AGN

Abstract

We have found empirically that the radio loudness of AGN can be understood as function of both the X-ray and optical luminosity. This way of considering the radio loudness was inspired by the hardness-intensity diagrams for X-ray binaries, in which objects follow a definite track with changes to their radio properties occurring in certain regions. We generalize the hardness-intensity diagram to a "disk-fraction luminosity diagram", which can be used to classify the accretion states both of X-ray binaries and of AGN. Using a sample of nearly 5000 SDSS quasars with ROSAT matches, we show that an AGN is more likely to have a high radio:optical flux ratio when it has a high total luminosity or a large contribution from X-rays. Thus, it is necessary to take into account both the optical and the X-ray properties of quasars in order to understand their radio loudness. The success of categorizing quasars in the same way as X-ray binaries is further evidence for the unification of accretion onto stellar-mass and supermassive compact objects.