Stellar kinematics in surveys and simulations

We study stellar motions in the Milky Way with N-body simulations and large astrometric samples from ESA's Gaia mission. We identify two kinematic populations for white dwarfs in the Solar neighbourhood. We also investigate the accreted halo and reveal two new structures. Finally, our simulations show that radial migration as a function of vertical action depends on disc mass.

The most impressive feature on the night sky is the Milky Way. Our home Galaxy is subject to several different dynamical processes which will change how the stars in it move for long periods of time, causing them to change their orbit or clump together. By understanding these stellar motions and the structures they present, we are then piecing together the history of our Galaxy and can match what we see to theories of galactic mergers or interactions with mighty spiral arms. In this thesis we do just that and use large samples of stars to identify different features in their velocities. We find previously unseen structures and populations in the data. We also simulate some of the interactions that can cause the stars move in and out of the Galaxy and find that the efficiency of this motion given a star's height above the Galactic disc depends on the strength of the disc of that Galaxy.