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Session 29 - Dynamical Evolution of Galaxies.
Oral session, Monday, January 13
The evolution of dense rotating systems is studied through the use of N-body simulations. The initial configuration for each experiment is an isotropic Kuzmin-Kutuzov model. Hernquist's tree code is utilized to simulate the dynamical evolution, with dynamical relaxation produced by the graininess of the low-N potential field. We have modified the code to simulate physical stellar collisions, stellar evolution, mass loss and remnant formation, and star formation. Material ejected though stellar mass loss was allowed to escape some systems and was reprocessed through star formation in others. Each system begins with an isotropic velocity dispersion at all r. In all systems the halo dispersion evolves toward a radially biased state. In systems containing a central black hole, the dispersion becomes tangentially biased in the core, whereas it remains isotropic in systems with no black hole.
Collisions occur primarily in the core and energy equipartition causes heavier stars to sink to the system center. Thus the highest mass stars are found in the core. In systems where ejecta are allowed to escape the system, mass loss from these heavy stars reduces the collision rate and reverses the contraction of the core. Collisions also tend to produce a single dominant stellar merger remnant, as opposed to a swarm of intermediate-mass stars. In cases where we have suppressed all processes except relaxation and physical collisions, objects with greater flattening produce larger dominant stars. Rotation has a mild effect on the core density profile; systems which are rotationally flattened show a slightly steeper profile than do spherical systems, in systems with and without central black holes. An initial power law mass spectrum also produces a steeper core profile than a system which initially contains equal mass stars.
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