Morphology and kinematics of cosmic web filaments

Due to the web-like distribution of matter in the Universe predicted by the standard theory of structure formation, haloes and the galaxies they host are expected to be embedded in diffuse gas structures which constitute the circumgalactic medium (CGM) and intergalactic medium (IGM). The characterisation of this gas is an important step in understanding the formation and evolution of galaxies, as it is this accreting gas which provides the fuel for star formation activity in the galaxies. While these gaseous structures have been studied extensively with pencil beam absorption studies, their diffuse nature severely hampers their detection as extended emission and thus the characterisation of their large scale properties. The almost ubiquitous detection of Ly-alpha emission from the CGM and IGM of bright quasars at z>2 provides the opportunity to directly study the physical characteristics of the gas through the emission powered by ionising radiation from the quasars. However, this is contingent upon knowledge of the quasar halo host mass. Unfortunately, existing constraints on quasar host halo masses from clustering studies, exhibit significant discrepancies around redshift z~3, where the majority of Ly-alpha nebulae have been observed. In the first part of this research, I introduce a novel method to constrain quasar halo masses by analyzing the line-of-sight velocity dispersion maps of Ly-alpha nebulae. Using MUSE-like mock observations from cosmological hydrodynamic simulations, I demonstrate that the kinematics of the Ly-alpha emitting gas is dominated by the gravitational potential of the host halo and that the velocity dispersion profiles of Ly-alpha emitting gas exhibit self-similarity with respect to halo mass when appropriately rescaled by the virial radius of their host haloes. I further show that radiative transfer effects do not alter the shape but only the normalization of these profiles. Applying this method to 37 observed quasar Ly-alpha nebulae at 3<z<4.7, I find that associated quasars are typically hosted by ~10^{12.16\pm0.14} Msun haloes, independent of redshift, aligning with clustering and cross-correlation results. In the second part, I extend the analysis by comparing the surface brightness values of the 37 Ly-alpha nebulae to mock observations generated from cosmological simulations under the assumption of maximal fluorescence. Confining the simulated nebulae to the specific halo mass range derived from the Ly-alpha kinematics in the first part, I constrain the density of Ly-alpha emitting gas. The analysis reveals that the cold CGM must reach densities of 1 - 10 cm^-3 with a broad distribution to explain observed surface brightness values. I propose mechanisms, including compressive flows, Kelvin Helmholtz instabilities, and turbulence-induced thermal instabilities, to account for the formation of cold, high-density clouds. While theoretical considerations imply that the surface brightness values of the nebulae should increase with redshift, I show that the observed surface brightness values in fact exhibit no discernible redshift evolution. This implies an increase in the width the cold gas's density distribution with time. As turbulence is a potential driver of the broadness of the density distribution, this suggests an enhancement of the turbulence in the cold CGM of bright quasars from z~4 to z~3.