Origin, Evolution, and Implications of Wavelike Motions in the Stellar Disk of the Milky Way

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Astronomical surveys that measure the positions and velocities of stars in the Milky Way allow us to learn about the dynamics of the Galaxy and the structure of its dark matter halo. My research group uses a combination of theory, simulations, and data analysis to explore and exploit these surveys. Beginning in 2012, our focus has been on the hypothesis that the stellar disk of the Milky Way exhibits vertical wavelike motions, that is, motions normal to its midplane. The impetus for this work was the discovery by me and my collaborators of asymmetries in stellar number counts with respect to the midplane and vertical bulk motions of nearby stars. Soon after, similar features were found by other researchers using different surveys. In addition, ripples or corrugations were discovered in the further out in the Milky Way's disk. One possibility is that these features were caused by the gravitational field of a passing satellite galaxy.******The goal of my research program is to search for new evidence of a perturbed disk and develop an understanding of vertical waves through theoretical analysis and simulations. In addition, my group will explore the implications of disk disequilibrium for key projects such as the determination of the Galactic gravitational potential and the amount of dark matter in the Solar Neighbourhood. In short, this endeavour, which we have dubbed Galactoseismology, aims to learn about the structure of the Galaxy and its environment by studying wavelike motions in the disk.******The discoveries described above were made with surveys that included astrometric measurements of hundreds of thousands of stars. The field of Galactic Dynamics is now focused on Gaia, a European Space Observatory that will measure 6D phase space coordinates for over one billion stars and thereby increase the number of stars with phase space measurements by a staggering 3-4 orders of magnitude. Already, Gaia's 2nd Data Release, which provides 6D measurements for 7M stars, has produced intriguing results, such as curious phase space spirals near the Sun. Phase space structures such as these provide a potentially powerful probe of the Galactic potential.******One thrust of my research will be to apply data science methods to the analysis of the Gaia data in an effort to uncover other features in the distribution of stars. These methods include kernel density estimation and ridge finding algorithms from the field of computer vision. My research program also uses N-body simulations of galaxies to test our hypotheses. The simulation snapshots are "observed" to generate mock data catalogs that can be compared with actual data. Simulations also provide an opportunity to test our understanding of galactic dynamics.******Graduate and undergraduate HQP will be involved in all aspects of my research program and will gain valuable training in theoretical astrophysics, computational methods, and data science.*****