Extreme ionised outflows are more common when the radio emission is compact in AGN host galaxies

TL;DR

This study finds that compact radio emission in AGN host galaxies is strongly associated with extreme ionised outflows, suggesting a link between young or frustrated radio jets and high-velocity gas ejections.

Contribution

It introduces a combined machine-learning and size measurement approach to classify radio sources and demonstrates the correlation between compact radio emission and extreme outflows in a large AGN sample.

Findings

Compact radio sources have twice the likelihood of broad [O III] components.

High-luminosity, compact radio AGN are nearly four times more likely to have >1000 km/s outflows.

Radio jets and lobes are prevalent in compact sources, indicating jets may drive outflows.

Abstract

Using a sample of 2922 z<0.2, spectroscopically-identified Active Galactic Nuclei (AGN) we explore the relationship between radio size and the prevalence of extreme ionised outflows, as traced using broad [O III] emission-line profiles in Sloan Digital Sky Survey (SDSS) spectra. To classify radio sources as compact or extended, we combine a machine-learning technique of morphological classification with size measurements from two-dimensional Gaussian models to data from all-sky radio surveys. We find that the two populations have statistically different [O III] emission-line profiles, with the compact sources tending to have the most extreme gas kinematics. When the radio emission is confined within 3" (i.e., within the spectroscopic fibre or ~<5kpc at the median redshift), there is twice the chance of observing broad [O III] emission-line components, indicative of very high velocity outflows, with FWHM>1000 km/s. This difference is most enhanced for the highest radio luminosity bin of log[L(1.4GHz)/(W/Hz)]=23.5-24.5 where the AGN dominate the radio emission; specifically, >1000 km/s components are almost four-times as likely when the radio emission is compact in this subsample. Our follow-up ~0.3"-1" resolution radio observations, for a subset of targets in this luminosity range, reveal that radio jets and lobes are prevalent, and suggest that compact jets might be responsible for the enhanced outflows in the wider sample. Our results are limited by the available, relatively shallow, all-sky radio surveys; however, forthcoming surveys will provide a more complete picture on the connection between radio emission and outflows. Overall, our results add to the growing body of evidence that there is a close connection between ionised outflows and compact radio emission in highly accreting `radiative' AGN, possibly due to young or frustrated, lower-power radio jets.