The earliest galaxies formed during the first billion years after the Big Bang, producing the energetic photons required to initiate the Epoch of Reionization. Resolved observations of these sources enable us to build a picture of the evolutionary path from primordial density fluctuations to the development of galaxies such as our own. Kinematic analysis is a key probe into the mass budget of galaxies, the interstellar medium (ISM) properties affecting star formation, and the physical processes ongoing within galaxies including accretion, minor and major mergers, turbulence and feedback driven by stars or active galactic nuclei (AGN). With the extraordinary synergistic capabilities of the Atacama Large (sub)Millimetre Array (ALMA) and the James Webb Space Telescope (JWST), we are in an unprecedented era of discovery in detecting primeval galaxies across a wide range of wavelengths and emission line tracers of the multiphase ISM. However, numerical simulations show that warm ionized gas and cold gas trace different regions of galaxies and yield different measurements of internal properties, leading to the question of how can we compare information obtained from varied tracers? Furthermore, how confident can we be in physically interpreting high redshift observations that often suffer from the complications of poor angular and spectral resolution? In this thesis, we address these challenges through kinematic analysis of realistic NIRSpec IFU mock observations derived from galaxies in the SERRA suite of cosmological zoom-in simulations. With these synthetic data we determine the robustness of dynamical information recovered from typical IFU observations, and test widely-used criteria for identifying disks and gaseous outflows at high redshift. We carry the lessons learned from this study into the second part of the thesis, where we present the first sample of galaxies from the Epoch of Reionization to have constraints on the cool gas kinematics and distribution and morphology of the dust-obscured star formation, alongside NIRCam and NIRSpec IFU PRISM observations. We examine the morphology of the stars, gas and dust, and perform kinematic fitting to reveal an intriguing diversity of dynamical classifications, including rotation-dominated and dispersion-dominated galaxies, turbulent disks, and galaxies with signatures of merging activity and outflowing gas streams.
S Phillips (Thu,) studied this question.