Denys Wilkinson Building, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH
Christopher Everett
From spherical cows to asymmetric dinosaurs: multi-scale modelling of astrophysical jets.
The modelling of astrophysical jets has traditionally taken one of two approaches: macroscopic or microscopic. The former examines the large-scale structure and dynamics (e.g. GRMHD), while the latter focuses on the small scales of particle interactions (e.g. one-/multi-zone models and PIC). Each approach captures only part of the picture, but both perspectives are required to fully describe how these jets are formed, launched, and emit the multi-messenger signals through which we observe them. To bridge these two approaches, I have been developing DIPLODOCUS, a framework for general particle transport, capable of the self-consistent inclusion of large-scale spatial structure and small-scale anisotropic particle interactions. This talk aims to give an overview of the framework, its capabilities, and its use in studying particle creation, interactions, and emissions within the acceleration region of an AGN jet.
Dr Katherine Savard
A holistic approach to jets from X-ray Binaries
Jets launched from compact objects are not only excellent probes of the exotic physics close to these objects, but also regulate feedback and energy transport across large scales and can act as cosmic laboratories for high energy physics. In particular, X-ray binaries (XRBs) provide unique opportunities to observe jets launching and interacting with their surroundings on ‘human' timescales. In this talk, I present work from my PhD where I use relativistic hydrodynamic simulations informed by radio observations of discrete jet ejecta launched from an XRB — these simulations provide insight into the mechanisms with which these jets decelerate, disrupt, pump energy into their surrounding, and accelerate particles to high energies. I present software to then transform these simulation snapshots into realistic radio images, creating an end-to-end study of this system. I will then discuss follow-up implications of this work, and talk about future projects I’ll be pursuing as part of my postdoc here at Oxford.
Dr Bohan Yue
New insights into the jet powering mechanism in radio quasars from the LOFAR Two-metre Sky Survey (LoTSS)
Galaxy evolution theories propose that feedback processes from active galactic nuclei (AGN) govern the growth of massive galaxies in our Universe. A key component of the AGN feedback is the injection of kinetic energy from radio jets, yet there is still a fundamental lack of understanding of why quasars, otherwise very similar, have such a wide range of radio jet powers, and the impact of radio jets. Using large samples from the LOFAR Two-metre Sky Survey (LoTSS) DR2 coupled with a Bayesian parametric model, we can statistically separate jet from host galaxy radio emission, measure the distribution of jet power as a function of quasar properties to investigate the powering mechanism of radio jets. Our new results show that all quasars host radio jets across a full range of powers, while their power is mostly governed by local activities. Our model allows us to redefine the radio AGN populations based on actual levels of jet activities, which unifies previously divergent results on the black hole mass impact on AGN jets. We found quasars hosting the most massive black holes show an enhancement in radio emission due to higher prevalence of powerful jets. We will demonstrate how the production of powerful jets is linked to the large-scale clustering and accretion modes of quasars. The combination of these results sets tight observational constraints on the launching mechanism of powerful radio jets in quasars. Our methodology holds great potential in revealing the emission mechanisms in fainter radio quasars to be discovered by SKA.