Large Surveys and Data-Driven Investigations of Radial Migration

Abstract: We probe the implications of 5 different previously developed models of the evolution of the Milky Way’s radial metallicity gradient for radial migration of stars observed today between 5kpc < R < 12kpc. Our sample contains 7167 giant stars, with metallicities and radial velocities obtained from APOGEE DR14, full 5-parameter kinematic information from Gaia DR2, and ages derived in Martig et al. 2016. Guided by the radial metallicity histories provided by these models, we are able to match stars with known age and metallicity to implied birth locations, using the fact that stars retain the metallicity of the medium from which they formed. The difference between the stars current radius and birth radius, R − RB , provides us with a metric for measuring migration distance. We are then able to conduct a meta-analysis—both qualitative and quantitative—of the migratory distances which result from the different models employed. We find that the results from each model are largely in good agreement, and their differences, if any, are subtle. In particular, we attempt to separate the effects of the two processes collectively called “radial migration”: blurring and churning. We find that churning causes large radial displacements early in a star’s lifetime, but both churning and blurring behave diffusively, and in similar magnitude, beyond this initial movement. Furthermore, the models collectively predict that a minimum 55% of stars have experienced churning, and that only 5% of stars remain at their birth radii today.