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Title:Simulations of active galactic nucleus feedback in the cores of galaxy clusters
Author(s):Lu, Yinghe
Director of Research:Ricker, Paul Milton
Doctoral Committee Chair(s):Ricker, Paul Milton
Doctoral Committee Member(s):Fields, Brian; Gammie, Charles; Shen, Yue
Department / Program:Astronomy
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):active galaxies
galaxy clusters
intracluster medium
numerical methods
Abstract:This thesis focuses on developing a new subgrid model and studying feedback from active galactic nuclei (AGN) using adaptive mesh refinement (AMR) hydrodynamics simulations of the cores of galaxy clusters. Modeling of feedback from AGN that consist of central super-massive black holes (SMBH) in galaxy clusters through simulations is a very challenging problem. Due to limited resolution to resolve physics at sub-resolution scales, previous studies usually involve a subgrid model and considerable simplification of the complex physics involved in the region surrounding the AGN. Inspired by recent theoretical and observational progress in better understanding many physical processes, I have developed a new sink particle method that incorporates black hole accretion and jet launching in a more physically realistic manner. In this model, I measure the accretion rate through an artificial control surface with an inner boundary condition that allows consideration of the accretion of cold gas blobs. The jet model includes the effect of precession to deposit feedback energy in a more distributed manner. With the model embedded in the AMR hydrodynamics code FLASH, I have conducted simulations of the central few kiloparsecs of the intracluster medium (ICM) in cluster cores. I address how jet precession interacts with turbulent motions in the ICM and determine whether it can help regulate accretion and feedback. I find that, while turbulent driving itself enhances the kinetic energy of the ICM and triggers accretion, with precessing jets and weaker turbulent driving the gas primarily passes through strong shocks produced by the jet, and cavity-like structures are formed. However, the situation changes with stronger turbulence: the jet material gets blown away, and the accretion process is enhanced by inflow of hot gas, allowing more energy to be deposited in the ICM. This coupling between jet precession and turbulent driving thus helps to regulate AGN feedback. I compare the new method and results with magnetohydrodynamic (MHD) simulations of jet production and propagation at smaller scales and discuss convergence with resolution and jet size. In addition, I further improved the method with consideration of accretion disk structure and accretion state transitions, and developed equilibrium models that can be incorporated into the subgrid physics module. I also discuss preliminary work regarding AGN jets interacting with shocks and cold fronts in the ICM, which are also important processes that occur in cluster cores. The results from this work have provided better understanding from a theoretical perspective of why most galaxy clusters with cool cores do not cool as rapidly as previously predicted, and lack evidence of recent star formation. I have answered questions regarding the details of AGN jets interacting with ICM gas, and how jets deposit energy from the SMBH in a isotropic manner. I also discussed how different heating mechanisms contribute to the heating and cooling balance in cluster cores. Future work will give more insights into the complex interplay of many interesting physics processes occurring in the centers of galaxy clusters.
Issue Date:2020-07-17
Rights Information:Copyright 2020 Yinghe Lu
Date Available in IDEALS:2020-10-07
Date Deposited:2020-08

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