Title: Cartography of the Milky Way

Abstract: I will provide an overview of the chemodynamic structure the Milky Way using large scale spectroscopic surveys such as APOGEE and GALAH combined with astrometric parameters from Gaia. The chemical structure of the Milky Way is highly variable with location in the disk: the inner Galaxy is dominated by super solar metallicity populations with solar alpha abundances close to the plane, while above the plane the inner Galaxy is dominated by metal poor and alpha enhanced populations that we often associate with the thick disk. However, in the outer Galaxy this picture is markedly different: the stars high above the plane are solar alpha and the same metallicity as those found in the plane, and the high alpha thick disk population is not observed. The shape of the metallicity distribution function (MDF) for stars close to the plane also varies with location: in the inner Galaxy, the MDF is peaked at high metallicities and is negatively skewed, while in the outer Galaxy the MDF is peaked at low metallicities and positively skewed. We find that radial migration is required to explain the change in skewness of the MDF with radius. We find that the velocity dispersion of the disk is a function of angular momentum, age, metallicity, and height above the plane, and in general varies smoothly as a function of these variables: there is no need for a distinct thick disk origin. Similarly, we find we can explain the chemical evolution of the Galaxy using an analytic model that incorporates radial migration, but no distinct thick disk component is required to explain the chemical abundance distribution of the disk. Using samples of stars with precise age estimates, we find a strong correlation between most elemental abundances and the age and overall metallicity of a star, with very little scatter in the relations aside from our measurement uncertainties. We find we are able to recover a stars age to ~1 Gyr from its chemical abundances alone, regardless of angular momentum. This implies that the age-metallicity-abundance relations we find are universal in the disk, and that the Milky Way must have fairly uniform abundances at a given radius as a function of azimuth.

Bio: My career has focused on mapping out the structure of the Milky Way using large spectroscopic surveys. I did my PhD at New Mexico State University working with the APOGEE survey. I later moved to the Observatoire de la Cote d'Azur for my first post doc, where I worked with data from the Gaia-ESO and AMBRE surveys. I am currently an ASTRO3D Fellow at the University of Sydney as part of the GALAH project.