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Title: Exploring galaxy clusters and groups with cosmological simulations
Author: Henden, Nicholas Alistair
ISNI:       0000 0004 7968 5806
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Galaxy clusters are the largest gravitationally-bound objects in the Universe, their unparalleled size providing powerful leverage to probe large-scale structure growth and cosmology. At the same time, clusters and groups of galaxies represent unique astrophysical playgrounds in which galaxies interact with each other and with the intervening gas, both of which are strongly influenced by a range of astrophysical processes such as star formation or feedback from supernovae and active galactic nuclei (AGN). In this thesis I present the 'Feedback Acting on Baryons in Large-scale Environments' (FABLE) project, a new suite of cosmological hydrodynamical simulations of galaxies, groups and clusters designed to further our understanding of the formation and evolution of these fascinating objects. Firstly I perform a detailed comparison of the FABLE simulations to low-redshift observations, demonstrating simultaneous agreement with observational constraints on the total stellar and gas mass contents of groups and clusters and the galaxy stellar mass function. I generate synthetic X-ray spectra for the simulated systems and find good agreement with a range of observed X-ray scaling relations. In addition I show that the radial gas profiles of FABLE groups and clusters are a good match to low-redshift observations. Residual deviations in the thermodynamic properties of the cluster core region suggest that more sophisticated AGN feedback modelling or additional physical processes may be needed to explain the observed properties of cluster cores. Next I extend the analysis of the cluster scaling relations out to high redshift, including a comparison to observational constraints and other simulation predictions. I find that all examined scaling relations deviate from the self-similar prediction in terms of their slope and redshift evolution. These deviations are attributed to a combination of factors, including non-thermal pressure support provided by kinetic motions in the intracluster gas and the effects of non-gravitational physics such as AGN feedback. I also find a significant variation in the scatter about the relations with changing halo mass and redshift, contrary to the assumptions of most observational studies. In addition I investigate the scaling between the Sunyaev-Zel'dovich (SZ) signal and total mass, showing good agreement with cluster data from 'Planck' and the South Pole Telescope over a wide redshift range. I demonstrate the sensitivity of the predicted number of detected clusters in an SZ-selected survey to the assumed SZ scaling relation using several recent observational and simulation constraints. Finally I investigate the halo mass and redshift dependence of the total baryon contents of FABLE clusters and groups and of the stellar mass, size and shape of brightest cluster galaxies (BCGs). In particular I show that the simulations agree with recent constraints on the (lack of) redshift evolution in the total gas and stellar mass of massive clusters. Furthermore, I use the stellar mass profiles of FABLE BCGs to highlight potential biases in observational studies of BCG growth associated with the assumed light profile and the outer radius of the fit.
Supervisor: Puchwein, Ewald ; Sijacki, Debora Sponsor: Science and Technology Facilities Council (STFC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: galaxies ; galaxy ; clusters ; cosmological simulations ; active galactic nuclei ; AGN feedback ; scaling relations ; cosmology ; BCG ; groups ; hydrodynamical simulations ; black holes ; intracluster medium