Description
Red quasars exhibit a higher incidence of compact (galaxy-scale or smaller) radio emission than blue quasars, arising from systems near the radio-loud/radio-quiet threshold. This result cannot be fully explained by the standard orientation model, instead favouring red quasars as a distinct phase in a quasar’s lifecycle, possibly an obscured-to-unobscured transition where low-power jets and/or AGN-driven winds drive away gas and dust. Previous work has focused on classifying radio morphologies of red and blue quasars in one radio frequency band, but radio emission can differ significantly across frequencies, with lower frequencies probing older electron populations.
For optically selected red and blue quasars, I compare radio morphologies across 3 surveys (FIRST: 1.4 GHz; VLASS: 3 GHz; LoTSS: 144 MHz) and find red quasars are significantly less likely than blue quasars to show extended low-frequency radio emission, suggesting fewer episodes of past activity and a younger evolutionary stage. Red quasars compact in all 3 surveys show the highest radio detection rates, and a striking excess over typical quasars of detections with steep radio spectral slopes $\approx -1$, consistent with an AGN-driven wind shock model. Additionally, I find a connection between the amount of dust and the production of radio emission, with the fraction of sources with shock-like radio spectral slopes increasing toward higher levels of dust extinction. I suggest these compact red quasars represent a young, “dusty blow-out” phase, where a compact jet and/or AGN-driven winds interact with a dusty ISM, causing shocks, leading to steep spectral slopes and enhanced radio detection rates.
