Radio-dust connection in quasars driven by powerful ionised outflows

Abstract

Feedback from dusty quasars is thought to be a key driver in galaxy evolution. Multiple studies have reported a link between dust extinction and radio emission in quasars, possibly attributed to winds or jets interacting with the interstellar medium. We use optical spectra from the Dark Energy Spectroscopic Instrument (DESI) to test whether ionised outflows could be driving the observed radio-dust connection and to determine whether dust and/or colour play a role in producing high-velocity ionised outflows in quasars. Based on a sample of 3418 DESI quasars at 0.5 < z < 0.9, we constrained the [OIII]$λ$5007 kinematics by fitting the spectra with PyQSOFit and comparing the observed trends among the [OIII] outflow velocity and the line-of-sight dust extinction E(B-V), optical-to-mid-infrared (MIR) colour g-W2, and L6$μ$m/L5100A (a proxy for MIR excess). Utilising radio data from the LOFAR Two-metre Sky Survey (LoTSS) DR2, we also explored the link between radio, dust, and outflows. We find that the link between radio emission and dust obscuration is driven by sources hosting high-velocity ionised outflows. However, we find no significant trend between the [OIII] outflow velocity and E(B-V), which suggests dust extinction alone is not a significant factor in determining whether a quasar hosts a powerful ionised outflow. On the other hand, we find a clear positive trend between g-W2 and outflow velocity, even after controlling for luminosity. We suggest this is due to a connection between a MIR excess (boosting the W2 band) and outflows, which is supported by a positive trend between L6$μ$m/L5100A and outflow velocity. Our results point to a scenario in which outflows shock the surrounding dust and gas, heating the dust and boosting both the MIR and radio emission.