|
“Mixing and Relaxation in Time-Dependent Collisionless Systems” Dr. Monica Valluri University of Michigan |
| Recent investigations of mixing during collisionless galaxy mergers shows that "violent relaxation" is primarily driven by compressive tidal shocks and dynamical friction. The former process heats particles, while the latter is responsible for the transfer of the orbital energy and angular momentum of the progenitors into the internal degrees of freedom of the remnant. I will show that both processes operate primarily during pericenter passages indicating that the transfer of energy does not occur due to continuous exchange of energy of particles with the time dependent potential. It has been known since the work of Taylor and Navarro (2001, ApJ, 563, 483) that the spherically averaged phase-spaced density profiles of dark matter halos resulting from cosmological N-body simulations have power-law profiles over 2.5 orders of magnitude. We investigate the origin of this profile by studying the evolution of coarse grained phase-space density of collisionless particles in two types of N-body simulations. First, we follow the evolution of phase space density in major mergers of NFW halos. We find that while major mergers preserve the power-law profiles over 2.5 orders of magnitude. We also investigate the evolution of phase-space density profiles obtained from cosmological N-body simulation. I will present results of our analysis which elucidates the importance of minor mergers in the formation of power-law phase-space density profiles. |