Description
Radial migration—a process that moves stars from their birthplaces to their present-day galactocentric radii—has been shown to play a crucial role in shaping the Milky Way disc, particularly based on age and metallicity measurements of stars in the solar neighbourhood. With Gaia DR3, we now have chrono-chemo-kinematic maps of the Milky Way that extend far beyond the solar neighbourhood, enabling us to distinguish between different radial migration mechanisms.
In this study, we focus on the observational signatures of radial migration driven by the expansion of the bar’s corotation resonance as the bar slows. Using a test particle simulation, we demonstrate that stars currently near the bar’s corotation radius can have two distinct origins: (1) inner disc stars that migrated outward via corotation resonance dragging, and (2) stars that formed locally. By applying a simple but physically motivated metallicity enrichment model, we successfully reproduce the observed age–metallicity patterns in the Galactic disc and their dependence on guiding radii. We further explore the implications of this migration mechanism on the chemical cartography of the Milky Way disc, including the [α/Fe]-bimodality and azimuthal metallicity variations. Because this mechanism is closely linked to the pattern speed evolution of the Galactic bar, we are also able to infer the bar's dynamical history: our results suggest that the bar formed approximately 6–8 Gyr ago with an initial pattern speed of 60–100 km/s/kpc, and has since decelerated by 50–70%.
