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Abstract

Observations and theoretical studies suggest that galaxies are surrounded by a halo of diffuse gas that extends far beyond the extent of the central stellar component. This region, known as the circumgalactic medium (CGM), serves as the area through which gas from larger scales accrete due to the gravitationally-driven growth of cosmic structures. Additionally, it contains gas that has been expelled from the galaxy due to feedback processes, as well as gas that circulates in the halo through recycling or fountain flows. The CGM is thus believed to be critically linked to the evolution of galaxies.

The non-trivial interactions of these various physical processes result in a complex structure within the CGM: while most of the volume is dominated by a warm-hot phase, there are also clouds of cooler gas that coexist. Despite significant progress over the recent past, many open questions remain regarding the origin of the multi-phase nature of this gaseous reservoir, its properties, and the role of different processes in shaping its existence. In this thesis, we explore various such puzzles using cosmological magnetohydrodynamical simulations run with \textsc{AREPO} and the IllustrisTNG galaxy formation model.

We begin by analyzing the publicly available TNG50 simulation, with a particular focus on Milky Way-like (MW-like) galaxies in most cases. Our findings suggest that, among other processes, feedback driven by galactic processes may significantly impact the CGM, including its overall temperature and velocity structure, the number of cold clouds, and the angular structure of magnetic fields. In the later parts of this thesis, we introduce and analyze the new GIBLE suite of simulations, also run with the same IllustrisTNG galaxy physics model, but exclusively simulating MW-like galaxies at ultra-high CGM gas mass resolutions. As a first scientific exploration with GIBLE, we study the draping of magnetic field lines around cold clouds -- a phenomenon simply absent in simulations run at lower resolutions, highlighting the power of these new numerical experiments.