Evolution of Extended Satellites in Massive Halos

Pierre Gravel

Doctor of Philosophy 1998
Graduate Department of Astronomy, University of Toronto

The evolution of extended satellites in massive halos is studied in the weak and the strong regimes of satellite deformation. In the first part of the thesis we follow the dynamics of a spherical region evolving locally as an Einstein-de Sitter universe containing overdensities acting as seeds for the formation of a satellite and its future host. We study the dynamics of forming satellites when their hosts are still unvirialized, accreting material, and generating time-varying gravitational potentials (TVGP). The three main dynamical processes affecting the satellite are dynamical friction, the TVGP, and tidal disruption. The internal flow of energy inside a satellite and across its boundary is analyzed with specialized local and global methods, providing information on the nature, the magnitude and the timing of the individual processes. A strongly deformed satellite able to survive a few galaxy crossings forms a compact core from which dynamical friction extracts energy, while its halo is tidally disrupted by the ``slingshot'' effect. This leads to the formation of systems of external stellar shells and internal energy shells. Their origins and appearances are closely related. Satellite self-gravity and phase wrapping control the emergence of both types of shells from the satellite inner regions once non-linear effects set in. In the second part of the thesis, we analyze the combined effects of dynamical friction, tidal stripping, and internal and external two-body heating on satellites moving inside massive hosts. External two-body heating is a stochastic process that occurs inside a satellite as a back reaction to the scattering of inhomogeneous material in the surrounding stellar system. This type of heating accelerates the evolution of less bound objects by increasing their rate of evaporation. The heating becomes important at low satellite velocities, and when the masses of the perturbing objects are comparable to or greater than the masses of the satellites. We determine how the interplay of dynamical friction, tidal stripping, and internal and external two-body heating drives the evolution of satellite populations and we apply these results to satellites inside dwarf galaxies.

Copied with permission by Marlene Cummins
May 15 1998