Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Physics and Astronomy

First Advisor

Joel E. Tohline


Three-dimensional hydrodynamic simulations show that, in the absence of self-gravity, an axisymmetric, gaseous galaxy disk whose angular momentum vector is initially tipped at an angle i0 to the symmetry axis of a fixed spheroidal dark matter halo potential does not settle to the equatorial plane of the halo. Instead, the disk settles to a plane that is tipped at an angle a = arctan [ q2 tan i0] to the equatorial plane of the halo, where q is the axis ratio of the halo equipotential surfaces. The equilibrium configuration to which the disk settles appears to be flat but it exhibits distinct nonaxisymmetric features. Whereas a purely stellar dynamical system in the same configuration would be destroyed by differential precession of the stellar orbits, the gaseous disk appears to be secularly as well as dynamically stable. This result has important implications for models of galaxy evolution because, over time, any stellar population that is formed from such an inclined disk should naturally fill a larger volume of space (form a "thicker disk") that surrounds the gaseous disk.