UC Santa Cruz

Galaxy rotation has been studied for over a century, using spectroscopic measurements to construct rotational models that describe the motions of their gas and stars. However, only a small subset of this work has recognized that galaxies are not entirely radially symmetrical, but are instead often disrupted in ways that simple velocity field models cannot capture. In this dissertation, I describe my work modelling nonaxisymmetric galaxy rotation and the astrophysical insights gained from these models.

Gravitational lensing distorts a galaxy's velocity field in a manner distinct from the distortions of its photometric shape, an effect called kinematic weak lensing. This allows for the construction of a model that uses this difference to extract lensing information about the system. I detail the properties and strengths of such a model, finding that for mock observations of source galaxies at moderate redshifts, the signal-to-noise of the lensing measurements improves by up to a factor of six over previous works, enabling the possibility of future lensing studies independent of current weak lensing systematic constraints.

I also describe the development of Nirvana, a Bayesian nonparametric velocity field fitting code designed to describe the bisymmetric motions present in barred galaxies. Using a sample of barred galaxies from the MaNGA survey, I construct the Nirvana-MaNGA sample, which is comprised of velocity field models of >1000 local barred galaxies, as well as a matched control sample of unbarred galaxies. Nirvana determines bar strength and location independent of imaging, providing an independent and direct test of dynamical models of higher-order noncircular motions in bars, agreeing with visual bar classifications on bar angle. I also find direct evidence of flattening in stellar population gradients along bar kinematic axes as compared to surrounding disk regions at the same radii, verifying results reliant on visual classifications and affirming the dynamic connection between the presence of bars and radial mixing of stellar populations.