I have studied the hot, diffuse gas around and between galaxies. Specifically, I have used the EAGLE numerical simulations of galaxy formation to predict the properties of this gas, and I have used... Show moreI have studied the hot, diffuse gas around and between galaxies. Specifically, I have used the EAGLE numerical simulations of galaxy formation to predict the properties of this gas, and I have used those properties to predict specific observables: soft X-ray absorption and emission lines. Measuring this gas is challenging, but if we can observe and characterise it, we can learn much about the gas flows in and out of galaxies that regulate their formation and evolution. Observations of soft X-ray lines with future X-ray telescopes, such as Athena and XRISM, will enable us to do so. For these future X-ray telescopes, the strongest X-ray absorption lines and essentially all detectable line emission will come from the gaseous haloes surrounding galaxies. Some weaker, but still detectable absorption lines will come from the more diffuse gas outside these haloes. Photo-ionisation by the intergalactic ultraviolet/X-ray radiation background affects the absorption and emission lines of the very diffuse gas between galaxies, and the diffuse edges of the galaxy haloes. Emission from this photo-ionised gas is not expected to be detectable, but some absorption should be. Show less
The gas around galaxies provides fuel for star formation, playing a crucial role in the formation and evolution of galaxies. However, because the gas is very diffuse, it is difficult to observe in... Show moreThe gas around galaxies provides fuel for star formation, playing a crucial role in the formation and evolution of galaxies. However, because the gas is very diffuse, it is difficult to observe in emission, so in this work we examine it by analyzing absorption lines in the spectra of bright background sources. Our observational results are also compared with current cosmological simulations. Show less
Galaxies grow by accreting gas, which they need to form stars, from their surrounding haloes. These haloes, in turn, accrete gas from the diffuse intergalactic medium. Feedback from stars and black... Show moreGalaxies grow by accreting gas, which they need to form stars, from their surrounding haloes. These haloes, in turn, accrete gas from the diffuse intergalactic medium. Feedback from stars and black holes returns gas from the galaxy to the halo and can even expel it from the halo. This cycle of gas inflow and outflow, its impact on star formation, and the detectability of the gas outside of galaxies are discussed in this thesis. The growth of galaxies and their gaseous haloes depends strongly on their mass, the age of the Universe, and the inclusion of feedback processes, as do their physical and observational properties. Show less
Over the past 15 years, the field of extragalactic astronomy has pushed to high redshift and our knowledge of natal galaxies has grown dramatically. Galaxies are now routinely detected at redshifts... Show moreOver the past 15 years, the field of extragalactic astronomy has pushed to high redshift and our knowledge of natal galaxies has grown dramatically. Galaxies are now routinely detected at redshifts z ! 6__7 (e.g. Bouwens et al. 2010; Labb_e et al. 2010; Oesch et al. 2010; Bouwens et al. 2011; McLure et al. 2011). However, there are fundamental concepts that are still poorly understood. How do galaxies get their gas? How does galactic feedback affect galaxy evolution? Show less
Over the past few decades, it has become evident that the vast amount of space that exists between galaxies contains trace amounts of elements heavier than helium ('metals' in astronomical terms).... Show moreOver the past few decades, it has become evident that the vast amount of space that exists between galaxies contains trace amounts of elements heavier than helium ('metals' in astronomical terms). This is surprising since the baryonic universe is expected to initially be composed of solely hydrogen, helium and very small amounts of lithium and beryllium. Metals are predicted to be exclusively associated with stars, which are extremely rare in the intergalactic medium. The aim is therefore to predict how the metals got there and what is their distribution throughout cosmic time. This work investigates these mechanisms using a suite of over 50 three-dimensional, hydrodynamic, computer simulations. After discussing how metals and background radiation can affect intergalactic gas and in turn galaxy formation/evolution in a significant way, the focus turns to the cosmic distribution of metals. The simulations predict that hot intergalactic gas contains a constant fraction of metals throughout most of the history of the universe, while the metal fraction of the cold phase is increasing. It closes by considering the origin of such metals, finding that low mass galaxies expel metals into the cold phase from early times. Show less
Polycyclic Aromatic Hydrocarbons (PAHs) are one of the most common chemical compounds on Earth. These big molecules are naturally present in crude oil and coal deposits, and are also formed by... Show morePolycyclic Aromatic Hydrocarbons (PAHs) are one of the most common chemical compounds on Earth. These big molecules are naturally present in crude oil and coal deposits, and are also formed by incomplete combustion of carbon-containing fuels, hence they are found in car exhaust, cigarette smoke and (too) well-cooked meats. This makes PAHs one of the most widespread organic pollutants. In space, PAHs are an important and ubiquitous component of the Interstellar Medium, dominating the mid-infrared emission of many astronomical objects. However, very little is known about the destiny of PAHs when they are bombarded by high-velocity ions and electrons arising from interstellar shocks, hot gas and cosmic rays (CRs). The research described in this thesis shows that in shocks with velocities above 100 km/s and in a million-degree gas, PAHs are completely destroyed by collisions with electrons, and can survive only if isolated in denser clouds. Destruction by CRs is due to collisions with ions. Because of their high energy (5 MeV - 10 GeV) CRs can access these denser clouds and will set the lifetime of those protected PAHs, which can be used as a __dye__ for tracing the presence of material entrained in the hot gas. Show less
