The Optical-Radio Mapping: the kinetic efficiency of Radio-Loud AGNs

TL;DR

This paper estimates the average kinetic efficiency of radio-loud AGNs by comparing optical and radio luminosity functions, finding a typical efficiency of around 1% and suggesting radio sources contribute significantly to black hole growth.

Contribution

It provides a novel empirical constraint on the kinetic efficiency of radio-loud AGNs using luminosity functions and Monte Carlo simulations, linking radio emission to black hole accretion.

Findings

Kinetic efficiency g_k ≈ 0.10 with scatter ~0.38 dex.

Radio sources contribute at least 25% to local black hole mass density.

Estimated kinetic efficiency ε_k ≈ 0.01 for jet/wind production.

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 L_k, empirically correlated to the radio emission. Thus in terms of the ratio g_k=L_k/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 g_k=0.10^{+0.05}_{-0.01} holds, with a scatter \sigma=0.38^{+0.04}_{-0.09} dex; with these values we also match a number of independent correlations between L_k, L and radio emission, that we derive through Monte Carlo simulations. We proceed to translate the value of g_k into a constraint on the kinetic efficiency for the production of radio jets or winds, namely, \epsilon_k=L_k/(Mdot*c^2)~0.01 in terms of the rate Mdot 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.