Unveiling the origin of the radio emission in radio-quiet quasars

TL;DR

This study uses VLBI observations to determine that at least some radio-quiet quasars have radio emissions primarily driven by active galactic nuclei, clarifying the origin of their radio signals.

Contribution

First direct VLBI evidence showing that the radio emission in some RQQs is dominated by AGN activity, not star formation.

Findings

3 out of 18 RQQs detected with VLBA at 1.4 GHz.

At least some RQQs have radio emission dominated by AGN.

First measurement of the AGN contribution fraction in RQQs.

Abstract

The origin of the radio emission in radio-quiet quasars (RQQs) has been a matter of debate for a long time. It is not well understood whether the emission is caused by star formation in the host galaxy or by black hole activity of the active galactic nuclei (AGN). We shed some light on these questions using the Very Long Baseline Interferometry (VLBI) technique to search for RQQs in the field of the Cosmological Evolution Survey (COSMOS). The extensive multi-wavelength coverage of the field (from radio to X-rays) was used to classify RQQs, and the milli-arcsecond resolution of VLBI provides a direct way to identify AGNs. In a sample of 18 RQQs we detected 3 using the Very Long Baseline Array (VLBA) at 1.4 GHz. In this letter we report for the first time on a sample of RQQs with a measured lower limit on the fraction of radio emission coming from the AGN, thus demonstrating that the radio emission of at least some RQQs is dominated by an AGN.