Dynamical Origins of Azimuthal Metallicity Variations in the Galactic Disk: Insights from Kinematic Ridges with Gaia

Abstract Kinematic and spectroscopic studies in the past few years have revealed coherent azimuthal metallicity variations across the disk of the Milky Way (MW) that may be the result of dynamical process associated with nonaxisymmetric features of the Galaxy. At the same time, stellar kinematics from Gaia have uncovered ridgelike features in the velocity space, raising the question of whether these chemical and dynamical substructures share a common origin. Using a sample of disk stars from Gaia Data Release 3, we find that azimuthal metallicity variations are correlated with kinematic ridges in the V ϕ – R plane, suggesting a shared origin. We utilize a suite of MW test-particle simulations to assess the role of transient spiral arms, the bar, and interactions with a Sagittarius (Sgr)-like dwarf galaxy in simultaneously shaping both chemical and kinematic substructures. Among the physical mechanisms explored, bar and spiral arm interactions are the ones that consistently reproduce both the chemokinematic features and alignment observed in the Gaia data. While our model of an interaction with a Sgr-like dwarf galaxy can also induce kinematic and metallicity substructure, the amplitude of the azimuthal metallicity variations is too weak, suggesting this is likely not the dominant influence. Although additional contributing processes cannot be ruled out, the azimuthal metallicity variations observed in Gaia are best explained by a dynamical origin. Our results support the view that azimuthal metallicity variations in the Galaxy are driven by similar dynamical mechanisms responsible for generating the kinematic ridges and comoving groups.