Outflow-related radio emission in radio-quiet quasars

Abstract

ABSTRACT In this work, we revisit the relationship between [O iii] line width w90 (as the indicator of active galactic nucleus outflow velocity) and the radio emission in radio-quiet quasars (RQQs) by employing a large sample of Type I quasars (∼37 000) selected from the Sloan Digital Sky Survey (SDSS) Data Release 16. By median stacking the radio images (to include the dominant fraction of individually radio non-detected RQQs) of Karl G. Jansky Very Large Array Sky Survey for subsamples of RQQs with different w90, our study demonstrates that the correlation between w90 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 resulting 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 interstellar medium. Meanwhile, the star formation rates traced by the flux ratio of [Ne v]/[O ii] emission lines display no dependence on w90 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 w90 could not be attributed to outflow-enhanced (positive feedback) star formation in the hosts. However, this also indicates that the outflows, though exhibiting robust correlation with radio power, produce neither positive nor negative feedback to the star formation in their hosts.