PhD thesis: On the diversity of O vi absorbers at high redshift

In this thesis, we systematically analyze the properties of intergalactic \Ovi absorbing gas structures at high redshift using optical spectra with intermediate ($\sim 6.6$ \kms FWHM) and high ($\sim 4.0$ \kms FWHM) resolution, obtained with UVES/VLT. We complement our analysis with synthetic spectra obtained from extensive cosmological simulations that are part of the OWLS project (Schaye et al. 2010). Our main conclusions are: 1) Both the observations and simulations imply that \Ovi absorbers at high redshift arise in structures spanning a broad range of scales and different physical conditions. When the \Ovi components are characterized by small Doppler parameters, the ionizing mechanism is most likely photoionization; otherwise, collisional ionization is the dominant mechanism. 2) The baryon- and metal-content of the \Ovi absorbers at $z\approx2$ is less than one per cent of the total mass-density of baryons and metals at that redshift. Therefore, \Ovi absorbers do not trace the bulk of baryons and metals at that epoch. 3) The \Ovi gas density, metallicity and non-thermal broadening mechanisms are significantly different at high redshift with respect to low redshift. In particular, non-thermal broadening mechanisms appear less important at high redshift as compared to low redshift, where the turbulence in the absorption gas might be significant. This, together with the result that \Ovi arises in different environments, embedded in small- and large-scale structures, indicates that \Ovi does not trace characteristic regions in the circumgalactic and intergalactic medium, but rather traces a gas phase with a characteristic transition temperature ($T\sim10^{5}$K). 4) The \Ovi absorbers at high redshift arise in gas with metallicities significantly higher than the surrounding environment, which suggests an inhomogeneous metal enrichment of the IGM.