Measuring the accretion rate and kinetic luminosity functions of supermassive black holes

Abstract

We derive accretion rate functions (ARFs) and kinetic luminosity functions (KLF) for jet-launching supermassive black holes. The accretion rate as well as the kinetic power of an active galaxy is estimated from the radio emission of the jet. For compact low-power jets, we use the core radio emission while the jet power of high-power radio-loud quasars is estimated using the extended low-frequency emission to avoid beaming effects. We find that at low luminosities the ARF derived from the radio emission is in agreement with the measured bolometric luminosity function (BLF) of AGN, i.e., all low-luminosity AGN launch strong jets. We present a simple model, inspired by the analogy between X-ray binaries and AGN, that can reproduce both the measured ARF of jet-emitting sources as well as the BLF. The model suggests that the break in power law slope of the BLF is due to the inefficient accretion of strongly sub-Eddington sources. As our accretion measure is based on the jet power it also allows us to calculate the KLF and therefore the total kinetic power injected by jets into the ambient medium. We compare this with the kinetic power output from SNRs and XRBs, and determine its cosmological evolution.