The radio sky harbours both galactic and extragalactic sources of arcminute- to degree-scale emission of various physical origins. To discover extragalactic diffuse emission in the Cosmic Web... Show moreThe radio sky harbours both galactic and extragalactic sources of arcminute- to degree-scale emission of various physical origins. To discover extragalactic diffuse emission in the Cosmic Web beyond galaxy clusters, one must image low–surface brightness structures amidst a sea of brighter compact fore- and background sources. Angularly separating the faint from the bright radio sky requires high-quality ionospheric calibration. This thesis introduces new advances in and investigations into ionospheric calibration, the degree-scale Milky Way foreground, and two sources of megaparsec-scale emission in cosmic filaments: giant galactic outflows and cosmological structure formation shocks. Giant galactic outflows (or ‘giant radio galaxies’) are generated by the jets of active supermassive black holes, and transport relativistic leptons, entrained atomic nuclei, heat, and magnetic fields from the centres of galaxies to their outskirts and beyond. These outflows embody the most energetic pathway by which galaxies respond to the Cosmic Web around them. Structure formation shocks around filaments are a generic, but still elusive, prediction of cosmological simulations and trace the gravitational flow of matter from proto-voids to filaments. Both phenomena inform on the strength, topology, and origin of magnetic fields in the Cosmic Web. Show less
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
