| Unraveling the structure and dynamics of elliptical galaxies (and of other hot stellar systems such as star clusters) is in general a difficult exercise. Because of the information lost in projection, as well as the immense freedom of possible configurations, galaxy models suffer from a variety of degeneracies and systematic uncertainties. Here we explore several different avenues for rigorously recovering the intrinsic properties of stellar systems, looking in particular at determinations of their shapes and of their masses.;First, we consider deprojection degeneracies in axisymmetric galaxies, whereby information is lost about a galaxy's intrinsic light distribution when it is projected onto the sky. We find that a galaxy can harbor significant dynamical substructures which are not easily detectable in projection.;Second, we analyze the isophote shapes of X-ray emissions from hot gas in the halos of triaxial galaxies. A difference in shape between the luminous and dark matter distributions can produce an X-ray isophote twist. Given different assumptions for the halo shapes, we examine the expected character of such twists. We also model the twist observed in the galaxy NGC 720.;Third, we study the dynamics of the central galaxies in gravitational lens systems---which can be used to determine the Hubble constant, H0. The lens models are subject to degeneracies which necessitate independent determinations of the mass of the central lens galaxy. Using representative kinematical data compiled from a set of nearby elliptical galaxies, and nonparametric dynamical models that allow for the full freedom of orbital types, we set constraints on the mass of the lens galaxy in Q0957+561, determining H0 to an accuracy of 16%.;Fourth, we examine the global-dynamics of the giant elliptical galaxy M87, using spatial and kinematical constraints from its stars and globular clusters, and robust dynamical models. We rule out a constant mass-to-light ratio model, and find evidence for the onset of the Virgo Cluster halo at large radii.;Fifth, we model the dynamics of the Sgr A* cluster of stars. By fitting measurements of the stellar line-of-sight velocities and proper motions, and including the systematic uncertainty in the orbital anisotropy, we rigorously constrain the mass of the central black hole. We also use statistical parallax to directly determine the distance to the Galactic center. |
