Accretion and star formation in 'radio-quiet' quasars

TL;DR

This paper investigates the origin of radio emission in 'radio-quiet' quasars, providing evidence that black-hole accretion, rather than star formation, predominantly contributes to their radio signals, with implications for galaxy evolution models.

Contribution

It demonstrates that accretion-related processes dominate radio emission in RQQs using far-infrared data, challenging previous star-formation-based explanations.

Findings

Black-hole accretion dominates radio emission in RQQs.

Radio emission correlates with optical luminosity of quasars.

Star formation contributes less to radio emission than previously thought.

Abstract

Radio observations allow us to identify a wide range of active galactic nuclei (AGN), which play a significant role in the evolution of galaxies. Amongst AGN at low radio-luminosities is the 'radio-quiet' quasar (RQQ) population, but how they contribute to the total radio emission is under debate, with previous studies arguing that it is predominantly through star formation. In this talk, SVW summarised the results of recent papers on RQQs, including the use of far-infrared data to disentangle the radio emission from the AGN and that from star formation. This provides evidence that black-hole accretion, instead, dominates the radio emission in RQQs. In addition, we find that this accretion-related emission is correlated with the optical luminosity of the quasar, whilst a weaker luminosity-dependence is evident for the radio emission connected with star formation. What remains unclear is the process by which this accretion-related emission is produced. Understanding this for RQQs will then allow us to investigate how this type of AGN influences its surroundings. Such studies have important implications for modelling AGN feedback, and for determining the accretion and star-formation histories of the Universe.