Cold gas dynamics of high-z galaxies with ALMA

The discovery of galaxies with regularly rotating discs at z > 4 has been a puzzling challenge to galaxy formation models that tend to predict chaotic gas kinematics in the early Universe as a consequence of gas accretion, mergers and efficient feedback. In this thesis, I investigated the dynamics of a diverse sample of galaxies at z = 4.5 and at z = 0.5 - 3.5 observed with ALMA using cold gas tracers such as [CII], CO and [CI]. I derived the gas kinematics of the galaxies using 3DBarolo to understand the level of rotational support and potential origins of turbulence in the discs. The rotation curves are generally flat and the galaxies show high ratios of ordered-to-random motion (V/sigma). I also modelled the rotation curves of the galaxies with mass models that take into account baryonic and non-baryonic mass components to study the mass and concentration of the dark matter halos in young disc galaxies. To reproduce the high circular speeds observed in the central regions of the galaxies, the models suggest that there must be massive bulges already in place or a combination of physical mechanisms and/or observational limitations at play which need to be explored in more detail. This study shows that early disc formation with a clear dominance of rotation with respect to turbulent motions is present across a variety of galaxy types.