Exploring the Connection between UV/Optical Variations and Radio Emission in Radio-Quiet Quasars: Clues on Radio Emission Origin

TL;DR

This study investigates the relationship between UV/optical variability and radio emission in radio-quiet quasars, revealing that more variable quasars tend to have weaker radio signals, challenging existing models of radio emission origins.

Contribution

First analysis of UV/optical variability's relation to radio emission in RQQs, suggesting independence from disc turbulence and potential star formation origins.

Findings

More variable RQQs show weaker radio emission.

Radio emission may be independent of disc turbulence.

Star formation could contribute to radio signals.

Abstract

The radio emission in radio-quiet quasars (RQQs) has been a long mystery and its physical origin remains unclear. In a previous work we find UV/optical more variable quasars have stronger X-ray emission, indicating a link between disc turbulence and X-ray corona heating. In this work, for the first time, we investigate the relation between UV/optical variability and the radio emission in RQQs selected from SDSS stripe 82 and FIRST radio survey. We median stack the FIRST images and detect clear signals from RQQs in the co-added images of individually radio non-detected sources. Controlling the effects of other parameters, including redshift, black hole mass, bolometric luminosity and Eddington ratio, we find more variable RQQs, which are known to be X-ray relatively brighter, show tentatively weaker radio emission, contrary to the linear X-ray/radio correlation if the radio emission is from or driven by the corona. The discovery also suggests that if the radio emission in RQQs is driven by AGN activity (such as weak jet), the underlying driving process is independent to the disc turbulence which drives UV/optical variability and probably also corona heating. Alternatively, the radio emission could be due to star formation in the host galaxies.