A Study on the Formation and Dynamics of Galaxies

Citation

Fillmore, James Arthur (1985) A Study on the Formation and Dynamics of Galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/b70x-qk59. https://resolver.caltech.edu/CaltechETD:etd-09082008-150750

Abstract

The first half of this thesis is a study on the growth of perturbations in the early universe which might lead to galaxies, clusters of galaxies, or regions void of galaxies.

The growth of self-similar perturbations in an Einstein-deSitter universe with cold, collisionless particles is investigated. Three classes of solutions are obtained; one each with planar, cylindrical, and spherical symmetry. The solutions follow the development of structure in both the linear and nonlinear regimes.

Self-similar spherical voids which develop from initially underdense regions are also investigated. The character of each solution depends upon the initial density deficit. Steep perturbations result in voids bounded by overdense shells with sharp edges.

The second half of this thesis details solutions of steady-state axisymmetric models of elliptical and disk galaxies, and considers which observable properties can be used as diagnostics of the kinematic configuration of the spheroidal component of these systems.

Two component mass models are fitted to surface brightness measurements and used to fit kinematic models to the velocity data. The models with constant mass-to-light ratios and isotropic velocity dispersions adequately fit the inner regions of spiral galaxies with three caveats:

(i) Several galaxies show significant differences between the two sides of the major axis in both their rotation rate and velocity dispersion. While the differences might be caused by non-axisymmetric potentials, variations in the line-of-sight extinction are a more likely cause.

(ii) The inner segment (R ≤ 1 kpc) of the emission line (gas) rotation curve falls below the predicted circular velocity derived from the stellar velocities. We rule out a variation in the mass-to-light ratio as a cause for this discrepancy because M/L would have to significantly decrease at small radii; this trend is opposite to typical expectations of M/L. Significant emission from gas produced by stellar mass loss, particularly planetary nebulae, which is not yet settled into the disk might explain this observation.

(iii) Some of the bulges are flatter than one would expect from their rotation rate assuming isotropic random motions, but this additional flattening could be caused by the disk potential.

Self-consistent solutions of the stellar hydrodynamic equations for systems with isodensity surfaces which are concentric oblate spheroids and have constant mass-to-light ratios are presented. Various kinematic configurations are constructed to develop observational diagnostics which can distinguish these configurations. Because the inclination and true flattening of each elliptical is indeterminable, several kinematically distinct configurations are indistinguishable. Observations can uniquely characterize only those galaxies which lie at certain kinematic extremes.

Thesis Files