Förster, Pascal Ulrich; (2024) Exploring the interplay of galaxies and their gaseous environments. Doctoral thesis (Ph.D), UCL (University College London).

Text PhD_Thesis_Pascal_U_Foerster_Final_Public.pdf - Accepted Version Access restricted to UCL open access staff until 1 February 2025. Download (50MB)

Abstract

Galaxies and their gaseous environments are characterised by a strong interconnection throughout cosmic history. In this thesis, we explore the effects that early galaxies have on their gaseous environments through ionising radiation, as well as the effects of later-time galaxies’ environments on galaxy evolution and scaling relations. The Lyman-continuum (LyC) escape fraction characterises how galaxies reionised the neutral Intergalactic Medium (IGM). Previous studies of low-metallicity, high star-formation Lyman-alpha emitting galaxies (LAEs) found LyC leakers and non-leakers to be near indistinguishable in gas-phase metallicities and stellar populations. We explore whether the leaker/non-leaker dichotomy is due to a non-uniformly ionised IGM through theory and observation: we observe 11 LAEs at redshift 2.2 for Hα, Hβ, [OIII] and [OII] emissions, and construct various photoionisation models to eventually match our observations. Changing perspective, we explore drivers of the scatter in the Galaxy Main Sequence (GMS). We construct an equilibrium model for galaxy evolution, and expand it to allow for variations in environment, stellar-to-halo mass relation, and time-dependent accretion rates. We use observational and theoretical data to build initial conditions of large model galaxy populations, and evolve them in time. We use a variety of observables to compare our results to observations. We finally analyse galaxy offsets from four scaling relations: the GMS, the mass-metallicity relation, the neutral (HI) and the molecular (H2) hydrogen gas-mass relations. We use the extended xCOLD GASS sample with direct HI and H2 measurements together with xGASS and SDSS to compare joint offsets from observational scaling relations to corresponding offsets in three cosmological simulations, SIMBA, EAGLE and Illustris TNG100. This allows us to perform our analysis in four bins of stellar mass and reveal differences between cosmological simulations and observations, as well as link conclusions from the simulations’ subgrid-models to the impact of different feedback processes on observed galaxies.

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