Speaker
Description
The most rapid and energetic SMBH growth in the Universe has occurred in luminous quasi-stellar objects (QSOs), the most powerful class of AGN, making them the perfect laboratories for observing galaxy–SMBH evolution. When we have an unobscured view of the accretion disc, which peaks in the UV, QSOs display very blue UV–optical colours. However, we have recently discovered a hidden, potentially dominant, population of QSOs, obscured by dust. These dusty QSOs are almost completely uncharacterised by previous spectroscopic surveys due to observing strategies that target sources with blue colours. However, dusty QSOs could represent an important short-lived transitional phase in the evolution of galaxies, as predicted by simulations (a “blow-out” phase). Utilising data from the Dark Energy Spectroscopic Instrument (DESI) we can now, for the first time, explore a statistically significant sample of these reddened QSOs. Combining DESI spectra with radio data from the LOFAR Two-metre Sky Survey DR2, we find a striking positive relationship between the amount of dust extinction and the radio detection fraction in DESI QSOs. This demonstrates an intrinsic connection between opacity and the production of radio emission in QSOs which is not likely due to enhanced star formation or powerful radio jets. In our latest study, we construct sensitive radio SEDs of 38 QSOs across 0.144-3 GHz frequencies, with additional ~kpc scale e-MERLIN imaging, in order to probe the origin of the enhanced radio emission in dusty QSOs. We find that dusty QSOs tend to display steeper radio spectral slopes compared to typical blue QSOs, which is likely due to outflow-driven shocks on the surrounding ISM. These results are consistent with dusty QSOs representing an important blow-out phase in the evolution of galaxies.
