Schwarzschild modelling of elliptical galaxies and their black holes
  This article describes the Schwarzschild orbit superposition method. It is
the state-of-the-art dynamical modelling tool for early-type galaxies. Tests
with analytic models show that masses and orbital anisotropies of not too
face-on galaxies can be recovered with about 15 percent accuracy from typical
observational data. Applying Schwarzschild models to a sample of Coma galaxies
their dark matter halos were found to be 13 times denser than those of spirals
with the same stellar mass. Since denser halos assembled earlier, this result
indicates that the formation redshift 1+z of ellipticals is about two times
higher than of spirals. Roughly half of the sample galaxies have halo assembly
redshifts in agreement with their stellar-population ages. Galaxies where stars
appear younger than the halos show strong phase-space density gradients in
their orbital structure, indicative for dissipational evolution and possibly
connected with secondary star-formation after the main halo assembly epoch. The
importance of considering dark-matter in dynamical models aimed to measure
black-hole masses is briefly discussed.
