Optical–Radio Mapping: the Kinetic Efficiency of Radio‐Loud AGNs

Abstract

We constrain the mean kinetic efficiency of radio-loud active galactic nuclei by using an optically selected sample for which both the optical and the radio luminosity functions (LFs) have been determined; the former traces the bolometric luminosity L, while the latter traces the kinetic power Lk, empirically correlated to the radio emission. Thus in terms of the ratio gk = Lk/L, we can convert the optical LF of the sample into a radio one. This computed LF is shown to match the directly observed LF for the same sample if gk = 0.10−0.01+0.05 holds, with a scatter σ = 0.38−0.09+0.04 dex; with these values we also match a number of independent correlations between Lk,L and radio emission, that we derive through Monte Carlo simulations. We proceed to translate the value of gk into a constraint on the kinetic efficiency for the production of radio jets or winds, namely, in terms of the rate of mass accretion onto the central black hole. Then, on assuming that on average the radio sources share the same kinetic efficiency, we compute a solid lower limit of about 25% on the contribution of radio sources to the local black hole mass density.