"The Radio Properties of Dusty Quasars"
ESO AGN Coffee Club
- Date: Apr 22, 2026
- Time: 02:30 PM - 03:30 PM (Local Time Germany)
- Speaker: Victoria Fawcett (ESO)
- Location: ESO Garching
- Room: Library
Abstract:
When we have an unobscured view of the accretion disc, which peaks in the UV, QSOs display very blue UV–optical colours. However, there exists an important population of QSOs, obscured by dust, which are typically uncharacterised by optical spectroscopic surveys. These dusty QSOs could represent an important short-lived transitional phase in the evolution of galaxies (a “blow-out” phase). Utilising data from 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 LoTSS 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 may be due to outflow-driven shocks. Exploring the radio morphologies and spectral slopes, we find that dusty QSOs typically have compact (small-scale) radio morphologies over 144 MHz, 1.4 GHz, and 3 GHz, which show an excess of steep-spectrum emission (α ≈ −1) not seen in normal blue QSOs or dusty QSOs with extended low-frequency radio emission. The strength of this excess steep-slope radio emission increases with increasing dust extinction, along with an overall increase in the radio-detection fraction. The majority of the dustiest QSOs with steep slopes have radio luminosities consistent with the prediction from a wind-shock model. These results support a picture in which compact, dusty QSOs are undergoing a blow-out phase, where an AGN-driven wind and/or compact jet interacts with a dusty ISM, causing shocks, leading to steep spectral slopes and enhanced radio detection rates.
When we have an unobscured view of the accretion disc, which peaks in the UV, QSOs display very blue UV–optical colours. However, there exists an important population of QSOs, obscured by dust, which are typically uncharacterised by optical spectroscopic surveys. These dusty QSOs could represent an important short-lived transitional phase in the evolution of galaxies (a “blow-out” phase). Utilising data from 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 LoTSS 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 may be due to outflow-driven shocks. Exploring the radio morphologies and spectral slopes, we find that dusty QSOs typically have compact (small-scale) radio morphologies over 144 MHz, 1.4 GHz, and 3 GHz, which show an excess of steep-spectrum emission (α ≈ −1) not seen in normal blue QSOs or dusty QSOs with extended low-frequency radio emission. The strength of this excess steep-slope radio emission increases with increasing dust extinction, along with an overall increase in the radio-detection fraction. The majority of the dustiest QSOs with steep slopes have radio luminosities consistent with the prediction from a wind-shock model. These results support a picture in which compact, dusty QSOs are undergoing a blow-out phase, where an AGN-driven wind and/or compact jet interacts with a dusty ISM, causing shocks, leading to steep spectral slopes and enhanced radio detection rates.