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

TL;DR

This study finds that azimuthal metallicity variations in the Milky Way are primarily caused by dynamical processes like bar and spiral arm interactions, which also produce kinematic ridges observed in Gaia data.

Contribution

The paper demonstrates a correlation between chemical and kinematic substructures and shows that bar and spiral interactions can reproduce these features in simulations.

Findings

Bar and spiral interactions reproduce observed chemo-kinematic features.

Sagittarius-like dwarf interactions are less effective in explaining metallicity variations.

Azimuthal metallicity variations are primarily driven by dynamical mechanisms.

Abstract

Kinematic and spectroscopic studies in the past few years have revealed coherent azimuthal metallicity variations across the Milky Way's disk that may be the result of dynamical processes associated with non-axisymmetric features of the Galaxy. At the same time, stellar kinematics from Gaia have uncovered ridge-like 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 DR3, we find that azimuthal metallicity variations are correlated with kinematic ridges in the V_phi-R plane, suggesting a shared origin. We utilize a suite of Milky Way test-particle simulations to assess the role of transient spiral arms, the bar, and interactions with a Sagittarius-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 chemo-kinematic features and alignment observed in the Gaia data. While our model of an interaction with a Sagittarius-like dwarf galaxy can also induce kinematic and metallicity substructure, the amplitude of the azimuthal metallicity variations are 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 that azimuthal metallicity variations in the Galaxy are driven by similar dynamical mechanisms responsible for generating the kinematic ridges and co-moving groups.