18 GIUGNO 2019 ore 11:00

New insights into AGN, via their radio emission

Dr. Sarah White (South African Radio Astronomy Observatory, Sudafrica)
New insights into AGN, via their radio emission

Radio observations allow us to identify a wide range of active galactic nuclei (AGN), which play a significant role in the evolution of galaxies. In the first part of this talk, I will escribe a new sample of powerful radio-galaxies, whose bright emission is detected at low radio-frequencies by the Murchison Widefield Array (MWA). This covers 72-231 MHz, and the 20 flux-densities over this range enable their broad-band radio spectra to be studied. Doing so highlights 'restarted' radio-galaxies, relic radio lobes, and sources with a spectral turnover that is likely due to free-free absorption by ionised gas. Identification of host galaxies is now complete, making this a highly-valuable legacy dataset. For the remainder of my talk, I will present recent analysis of radio emission from ‘radio-quiet’ quasars (RQQs). Being at low radio-luminosities, it has been assumed that their emission is dominated by star formation. However, using multi-wavelength data for two samples, we find support that black-hole accretion makes a significant contribution to the total radio emission in RQQs. These studies have important implications for modelling AGN feedback, and for determining the accretion and star-formation histories of the Universe.