Title: New insights into active galaxies, via their radio emission

Speaker：Sarah White (SARAO)

Time：3:00 pm Oct. 18th (Wednesday)

Zoom: 880 4627 4894 password: 6360

Abstract：

Radio observations allow us to identify a wide range of active galactic nuclei (AGN), which play a significant role in the evolution of galaxies. However, when it comes to studying their properties as a function of redshift and/or environment, the most-detailed studies tend to be limited by small-number statistics. In the first part of this talk, I will describe the G4Jy Sample (White et al. 2020a, 2020b; https://github.com/svw26/G4Jy) -- a collation of the brightest radio-sources in the southern sky (Dec. < 30 deg) -- whose bright emission is detected at low radio-frequencies using the Murchison Widefield Array. This instrument is the precursor telescope for the low-frequency component of the Square Kilometre Array, and allows us to select radio galaxies in an orientation-independent way (i.e. minimising the bias caused by Doppler boosting, inherent in high-frequency surveys). 140 G4Jy sources have been observed using Open Time on MeerKAT (PI: White; Sejake et al., 2023), and I will also describe follow-up using ATCA, the VLA, and SALT. With over 10 times as many sources as the best-studied, low-frequency radio-source sample that is optically complete (the revised Third Cambridge Catalogue of Radio Sources; 3CRR), the G4Jy Sample will allow models of powerful AGN to be tested more robustly. For the remainder of my talk, I will present analyses of radio emission from ‘radio-quiet’ AGN (White et al., 2015, 2017, in prep.). Being at low radio-luminosities, it has been assumed that their emission is dominated by star formation. However, using multiwavelength data, we find controversial evidence that black-hole accretion makes a significant contribution to their total radio emission. These studies have important implications for modelling AGN feedback, and for determining the accretion and star-formation histories of the Universe.

CV：

Dr Sarah White first enjoyed learning about radio astronomy as an undergrad at the University of Cambridge, then used it to study quasars for her PhD at the University of Oxford. Her first postdoc took her to Australia, where she used the Murchison Widefield Array, and in 2018 she started a SARAO Fellowship (affiliated with Rhodes University), using MeerKAT to continue her research into active galaxies. In addition to her former roles within the AfAS Early-Career Sub-Committee and the European Astronomical Society’s Inclusion Working Group, she is a keen climate activist as part of Astronomers for Planet Earth (A4E), and a social-justice advocate.