Construction and stability of disk galaxies, and the radial migration of their stars

Abstract

This thesis studies the stability of disk galaxies and the radial migration rate of their stars in self-consistent cosmological models of the formation of Milky Way-sized galaxies. In order to carry out appropriate numerical experiments, we first develop a new method for creating multi-component N-body galaxy models in a stationary state. Unlike previous techniques, this approach can flexibly cope with nearly arbitrary axisymmetric density distributions, and allows the construction of disk galaxy models with distribution functions that have three integrals of motion. To demonstrate the capability and accuracy of our parallel code GALIC in which we implemented the method, we examine 20 different galaxy models and study their stability when evolved as a live N-body system, finding very good results. We then apply the method to study the evolution of thin disk galaxies inserted in high-resolution dark matter halos drawn from the Aquarius simulation suite. The galaxy models are constructed with GALIC and are adiabatically grown in the evolving dark matter halo from redshifts z = 1:3 to z = 1:0, and then evolved live for a period of about 6 Gyrs to the present epoch. Our analysis of the simulations explores to what extent the galaxies are affected by the dark matter halo’s triaxiality and the large number of dark matter subhalos orbiting in it, and by how much the disk orientation is tumbling during this evolution. Finally, we study the radial migration of stars in hydrodynamical simulations of the same Milky Way-sized galaxies, carried out with the novel moving-mesh code AREPO. We are especially interested in the question whether radial migration can strongly modify metallicity gradients and the age-metallicity relation in such galaxies, and whether it can potentially contribute to the formation of a thick disk component.