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Dynamics and radio properties of AGN jets in complex environments

Yates-Jones, PM ORCID: 0000-0003-2806-3495 2021 , 'Dynamics and radio properties of AGN jets in complex environments', PhD thesis, University of Tasmania.

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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∘ 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 < 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

Item Type: Thesis - PhD
Authors/Creators:Yates-Jones, PM
Keywords: Active galactic nuclei, black holes, AGN feedback, galaxy evolution, hydrodynamical simulations
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Copyright 2021 the author

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