Exploring the properties of hot haloes around simulated galaxies

Abstract

The existence of hot, accreted gaseous coronae around massive galaxies is a central prediction of galaxy formation models in the ΛCDM cosmology. While observations now confirm that extraplanar hot gas is present around late-type galaxies, the origin of the gas is uncertain. We investigate the origin and properties of the hot gas that surrounds galaxies in the cosmological hydrodynamical EAGLE simulations. In summary, we find that haloes of Milky Way-mass and above host hot, accreted atmospheres as predicted by White & Frenk (1991). However, supernovae heated gas (feedback) in the innermost region of the halo typically dominates the X-ray emission.

Modern hydrodynamical simulations model various physical processes in the real Universe; however, many are included using 'subgrid models'. Although subgrid models have successfully modelled feedback effects, it remains unclear if, and by how much, the differing implementations affect other halo properties. This thesis uses 'zoom-in' simulations of a Local Group-like region evolved with both the Auriga and Apostle galaxy formation models. We find that feedback processes can be classified into two broad categories: 'ejective' and 'preventative', and future observations may constrain these two regimes.

The large dynamic mass range makes it computationally expensive to run simulations of galaxy formation. Therefore, we explore the basis function expansion technique (BSE), which can efficiently approximate the potential of a simulated galactic halo. We demonstrate that the Herquinst-Ostriker BSE can successfully reproduce the orbits of particles taken from n-body simulations. We also describe two further developments, including the addition of a thin, time-dependent disc and a method to model massive satellite galaxies within the halo efficiently.