Dynamics and radio properties of AGN jets in complex environments
Creators: name: Yates-Jones, PM
Publisher: name: University Of Tasmania
Year: 2023

description: Active Galactic Nuclei (AGN) feedback is a key ingredient in galaxy formation and evolution. A large portion of this feedback is done by radio jets in the form of shock-heating and uplifting gas. Both theory and observations show that jets are affected by their environment; therefore to understand jet feedback, a detailed understanding of jet-environment interaction is required. Analytic and semi-analytic models can predict jet dynamics and large-scale morphology but necessitate simple assumptions about both the environment and jet stability. These assumptions are contrary to observations,which show that radio jets exist in a range of environments,including both near and far from the centres of both relaxed and non-relaxed galaxies, groups and clusters. Numerical simulations of radio jets allow those assumptions to be relaxed. I have developed a jet simulation model based on the PLUTO code for (relativistic)-hydrodynamics that supports three-dimensional, relativistic, initially conical jets, which is the basis for the results presented in this thesis. Using this model, I focus on the dynamics, feedback, and radio properties of jets in non-idealised environments. To begin with, I investigate the role environment richness and intermittency play in radio jet evolution, by simulating two-dimensional, non-relativistic jets in poor group and cluster environments with varying intermittency properties. I show that the environment into which a radio jet is propagating plays an important role in the resulting morphology, dynamics and observable properties of the radio source. The same jet collimates much later in a poor group compared to a cluster, which leads to pronounced differences in radio morphology. The intermittency of the jet also affects the observable properties of the radio source, and multiple hotspots are present for multiple outburst jets in the cluster environment. I quantify the detectability of active and quiescent phases and find this to be strongly environment-dependent, concluding that the dynamics and observational properties of jets depend strongly on the details of energy injection and environment. Next, I present relativistic three-dimensional simulations of high-power radio sources propagating into asymmetric cluster environments, removing the spherically symmetric assumption typically used in the literature. I offset the environment by 0 or 1 core radii (equal to 144 kpc), and incline the jets by 0, 15, or 45‚Äöv†v= away from the environment centre. The different environment encountered by each radio lobe provides a unique opportunity to study the effect of environment on otherwise identical jets. Synthetic radio observables are derived from the purely hydrodynamic simulations assuming a constant departure from equipartition for the magnetic and thermal energy densities. I find that the jets propagating into denser environments have consistently shorter lobe lengths and brighter hotspots, while the axial ratio of the two lobes is similar. I also reproduce the observed anti-correlation between lobe length asymmetry and environment asymmetry at redshifts &lt; 0.3, confirming that observed large-scale radio lobe asymmetry can be driven by differences in the underlying environment. Simulations of radio jets are often used to make predictions for radio observables, providing the basis for observer interpretation. I have developed a method for calculating synthetic synchrotron emission from purely hydrodynamic simulations including both adiabatic and radiative losses, by incorporating Lagrangian tracer particles into the Eulerian jet fluid flow. These tracer particles are advected by the jet, and the local fluid history for each particle is recorded. In post-processing, this history is used as input to a lossy analytic emissivity model to calculate the emissivity as a function of frequency, redshift, and fluid history. Calculating the emission in post-processing provides increased flexibility for emissivity parameters like the source redshift and observing frequency. I apply this method to the three-dimensional relativistic simulations in asymmetric environments to investigate the effects of environment asymmetry on the observed broadband radio properties for each lobe. Finally, I present the foundations of CosmoDRAGoN, a large-scale project that will simulate the largest ever suite of double-lobed radio AGN in cosmological environments. Using simulated galaxy clusters taken from the three hundred cosmological simulation collaboration as the initial conditions for these simulations, I propagate relativistic three-dimensional conical jets into these cosmological environments. I compare the different jet morphologies produced based on the initial parameters, and show the impact of large-scale environment and cluster weather on jet evolution and observable broadband radio spectra for both active and remnant radio sources.