Outflow-related radio emission in radio-quiet quasars

Abstract

In this work, we revisit the relationship between [O III] line width $w_{\rm 90}$ (as the indicator of AGN outflow velocity) and the radio emission in RQQs by employing a large sample of Type I quasars ($\sim 37,000$) selected from the Sloan Digital Sky Survey (SDSS) Data Release Sixteen. By median stacking the radio images (to include the dominant fraction of individually radio non-detected RQQs) of Karl G. Jansky Very Large Array (VLA) Sky Survey (VLASS) for subsamples of RQQs with different $w_{\rm 90}$, our study demonstrates that, the correlation between $w_{\rm 90}$ and radio emission in our SDSS RQQs is significant, and remains solid after controlling the effects of black hole mass, quasar luminosity, Eddington ratio and redshift. This intrinsic link supports that the [O III] outflows in quasars, most likely resulted from wide-angled sub-relativistic quasar winds launched from the accretion disc, could make a dominant contribution to radio emission in the general RQQs. Alternatively, the correlation may be attributed to low-power jets in RQQs if they are ubiquitous and could efficiently enhance the [O III] width through interacting with the ISM. Meanwhile, the star-formation rates traced by the flux ratio of [Ne V]/[O II] emission lines display no dependence on $w_{\rm 90}$ after controlling the effects of black hole mass, quasar luminosity, Eddington ratio and redshift. This suggests that the stronger radio emission in RQQs with larger $w_{\rm 90}$ could not be attributed to outflow enhanced (positive feedback) star formation in the hosts. However, this also indicates the outflows, though exhibiting robust correlation with radio power, produce neither positive nor negative feedback to the star formation in their hosts.