Observational disk dynamics of late-type galaxies

The primary concern of this thesis is the robust measurement of the stellar velocity ellipsoid (SVE) in galaxy disks. We provide a detailed discussion of the empirical measurement and associated errors---random and systematic---for SVE measurements. The SVE has profound relevance for studies of galaxy disk dynamics as it quantifies, in gross terms, the stellar phase-space distribution function. While observationally expensive for most instruments, the SparsePak integral-field unit is well-suited to measuring line-of-sight kinematics in the low-surface-brightness, low-velocity-dispersion regime presented by galaxy disks and used to great effect in this study. We select a subsample of Disk-Mass Survey galaxies to: (1) Measure ionized gas kinematics from which we primarily determine the galaxy-disk projection parameters and the circular speed of the galaxy potential; (2) Determine the stellar kinematics via a new approach to the cross-correlation method that is more appropriate to the reality of limited spectral coverage; and (3) Characterize the SVE using a set of six decomposition methods generated via four well-established empirical and dynamical relations prevalent in the literature and in the theory of galactic stellar dynamics. These analyses demonstrate: (1) Our cross-correlation approach avoids 10% systematic errors in the nominal method used in the literature. (2) The six SVE modeling techniques we have developed are, on the whole, successful in describing the kinematics of the seven galaxies studied herein. (3) We find general agreement with the results of the few previous studies of the SVE shape; however, we do not confirm a trend in disk temperature with Hubble type. (4) Using the Toomre stability criterion, we find two of seven galaxies are unstable. (5) Contrary to expectation, we have discovered a positive correlation between the disk-mass fraction of a galaxy with the vertical velocity dispersion. This correlation suggests galaxies with larger total mass have less-dense and less-maximal disks compared to less massive galaxies in our sample. Finally, (6) We find a nearly constant line-of-sight velocity dispersion in the extended parts of at least three of the galaxies studied, implying an increase in the mass-to-light rats by factors of a few at these radii.