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Session 29 - Dynamical Evolution of Galaxies.
Oral session, Monday, January 13
Elliptical galaxies can be divided into two distinct types: faint ones with steep central profiles, called power laws, and bright ones with nearly flat central profiles, called cores. The role that mergers play in the evolution of this apparently bimodal population is poorly understood. In particular, it is not certain that the observed core population is sustainable after stellar mergers with power law galaxies. We present here extensive simulations of purely stellar mergers of galaxies selected from the set of Fundamental Planes that describe both the galaxy center and the galaxy as a whole. The large dynamic range in density between the two galaxy types makes this an expensive problem to investigate with a traditional N-body approach. We have therefore developed an efficient technique which is well-suited to simulate mergers of systems with widely varying densities. This technique takes advantage of the high density of the power law galaxy by approximating this galaxy as a point particle in the frame of the accretor. In this frame, dynamical friction acts upon this point galaxy and causes its orbit to decay. The accreted galaxy can then be followed in a separate simulation that includes the external force of the accretor galaxy on the accreted. These simulations suggest that the higher density of power law galaxies allows them to sink, nearly intact, to the center of a core galaxy and fill in the central core profile. To date, our experiments show that core survival requires more than the dynamics of visible stars. We present this purely stellar case as the first step in understanding the persistence of the Fundamental Plane for galaxy cores.
Program listing for Monday