Radio Loudness of AGNs: Host Galaxy Morphology and the Spin Paradigm

TL;DR

This study reveals two distinct sequences of AGN radio-loudness linked to host galaxy type, suggesting black hole spin and host galaxy properties influence jet production efficiency, with implications for understanding AGN radio emission.

Contribution

It demonstrates a host galaxy-dependent radio-loudness dichotomy in AGNs and proposes black hole spin as a key factor in jet power, advancing the understanding of AGN radio properties.

Findings

Two distinct radio-loudness sequences linked to galaxy morphology.

Radio-loudness increases as Eddington ratio decreases.

Black hole spin, influenced by galaxy type, likely governs jet power.

Abstract

We investigate how the total radio luminosity of AGN-powered radio sources depends on their accretion luminosity and the central black hole mass. We find that AGNs form two distinct and well separated sequences on the radio-loudness - Eddington-ratio plane. We argue that these sequences mark the real upper bounds of radio-loudness of two distinct populations of AGNs: those hosted respectively by elliptical and disk galaxies. Both sequences show the same dependence of the radio-loudness on the Eddington ratio (an increase with decreasing Eddington ratio), which suggests that another parameter in addition to the accretion rate must play a role in determining the jet production efficiency in active galactic nuclei, and that this parameter is related to properties of the host galaxy. The revealed host-related radio dichotomy breaks down at high accretion rates where the dominant fraction of luminous quasars hosted by elliptical galaxies is radio quiet. We argue that the huge difference between the radio-loudness reachable by AGNs in disc and elliptical galaxies can be explained by the scenario according to which the spin of a black hole determines the outflow's power, and central black holes can reach large spins only in early type galaxies (following major mergers), and not (in a statistical sense) in spiral galaxies.