Galactic dynamics in the era of Gaia

Abstract

In this thesis we study the kinematics and dynamics of our Galaxy, the Milky Way. We use data from the Gaia space telescope, which measures the positions and velocities of the Milky Way stars with unprecedented accuracy. Under assumption of the standard laws of gravity and by using the first data release of Gaia (September 2016), we are able to confirm the need for dark matter near the position of the Sun. More specifically we make a measurement of the local dark matter density. With the second data release of Gaia (April 2018) we characterise the velocity distribution of a large part of the Milky Way disk. We specifically look at the correlations between the velocity components since these are known to be sensitive to the mass distribution of the Galaxy. Within the uncertainties the correlations can be consistent with a spherical symmetric mass distribution. By studying the orbits of the stars available in Gaia DR2, we find that structures in spaces showing orbital parameters are not necessarily due to merger debris from external stellar systems. Instead, we show that typical galaxy mass distributions can naturally cause these structures. The dwarf spheroidal galaxies, satellite galaxies of the Milky Way, are thought to be highly dark matter dominated. Most studies, however, assumed that they are spherical, whereas observations show that they are not. For a specific test case we show that the mass can still be reliably measured. It is, however, not possible to retrieve the shape of the mass distribution.