Speaker
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. With the advent of SKA pathfinders such as LOFAR, we can probe lower radio frequencies than ever before, at high resolution and high sensitivity, while still retaining large sample sizes for population statistics.
For optically selected red and blue quasars, I compare radio morphologies across three 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 three 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 will discuss the implications within the context of a potential quasar evolutionary model and outline future research directions with SKA to further constrain the origin of enhanced radio emission in red quasars.
