The circumgalactic medium of Milky Way-Mass Galaxies

Hannington, Andrew 2024. The circumgalactic medium of Milky Way-Mass Galaxies. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

In recent decades, large-scale galaxy surveys have advanced our understanding of galaxy evolution. Investigating interactions between the interstellar medium (ISM) and intergalactic medium (IGM) through the baryonic matter surrounding galaxies – referred to as the Circumgalactic Medium (CGM) for Milky Way-mass (10^12 M_solar) haloes – may provide insights into astrophysical processes such as star formation, cosmology, and the formation of large-scale structures like the Cosmic Web. This thesis focuses on studying the CGM using numerical simulations. Numerical simulations of galaxy formation often produce distinct multiphase CGM structures and evolutionary histories, despite broadly agreeing with observed galaxy properties. These discrepancies suggest the underlying models yield degenerate solutions. To better understand the CGM, predictions from different simulations must be compared. This thesis analyses the evolution of the multiphase CGM in Auriga cosmological zoom simulations. Using Monte Carlo Tracer Particles, I explore how evolutionary processes vary with gas temperature and galactocentric radial distance. I find similarities in the evolution of cool (T ~ 10^4 K) and warm (T ~ 10^5 K) CGM, with the impact of feedback-driven outflows diminishing with radius, and the impacts of satellite stripping increasing with radius. Hot gas (T ~ 10^6 K) in the outer CGM is volume-filling and its evolution is governed by feedback-driven outflows. The hot CGM plays an unexpected, significant role in the evolution of cooler phases. I analyse novel simulations combining Surge resolution enhancements, the Auriga galaxy model, and two cosmic ray (CR) feedback models to investigate non-thermal CR feedback. Models incorporating CR energy dissipation show negligible changes in CGM properties compared to standard Auriga simulations. However, CR models lacking energy dissipation produce a denser, colder inner CGM with reduced multiphase structure and limited gas mixing. Finally, I present novel resolution enhancement methods building upon the Surge project. These methods achieve convergence with resolution in CGM density, temperature, and magnetic field strength. However, results for neutral hydrogen column density remain inconclusive, possibly due to adverse impacts on interactions between the hot and cool CGM phases.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Astronomy, galaxies: evolution, galaxies: formation, galaxies: haloes, intergalactic medium, circumgalactic medium, cosmic rays, methods: numerical, hydrodynamics, MHD
Funders:	STFC
Date of First Compliant Deposit:	13 January 2025
Last Modified:	14 Jan 2025 14:54
URI:	https://orca.cardiff.ac.uk/id/eprint/175207

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