Astro Seminar
Relativistic flow on the largest scales: jets in radio galaxies
Speaker: Robert Laing (SKAO)
Date: Wednesday 15 December 2021
Time: 14:00
Venue: Zoom
Jets - fast, highly-collimated, bipolar outflows - are inextricably linked to the processes of accretion and collapse onto compact astrophysical objects. They are observed most spectacularly in the the subject of this talk, radio galaxies. Radio-galaxy jets are intrinsically relativistic flows, with initial speeds approaching c. Not only can they be the primary channel of energy loss from accreting supermassive black holes, but they also have a major impact on their surroundings, and act as accelerators of the most energetic photons (and perhaps hadrons) we observe. I will start by reviewing recent advances in our understanding of jet launching (from theory and millimetre VLBI imaging), fuelling and feedback on galactic scales (from multiwavelength observations). I will then concentrate on observations and modelling of relativistic jets on large scales (up to ~100 kpc). Deep, high-resolution radio imaging (in total intensity and linear polarization), modelled with simple physical assumptions, can provide a wealth of information about the geometry, velocity field, emissivity and magnetic structure of the jets. I will contrast the properties of jets which flare, entrain, and decelerate (which we have previously studied in detail) with those which remain fast and narrow until they terminate. Modelling of the latter class requires the higher resolution and sensitivity of the new generation of radio interferometers and I will digress briefly to describe some of the technical subtleties. I will present a case study with the Jansky VLA which has revealed relativistic bulk flow with a persistent transverse velocity structure out to at least 140 kpc from the central black hole in the radio galaxy NGC 6251 and discuss the implications for jet composition and energetics. In conclusion, I will speculate on future observational prospects, particularly with the SKA.