Migration and Mixing in the Galactic Disc from Encounters between Sagittarius and the Milky Way

Abstract

Stars born on near-circular orbits in spiral galaxies can subsequently migrate to different orbits due to interactions with non-axisymmetric disturbances within the disc such as bars or spiral arms. This paper extends the study of migration to examine the role of external influences using the example of the interaction of the Sagittarius dwarf galaxy (Sgr) with the Milky Way (MW). We first make impulse approximation estimates to characterize the influence of Sgr disc passages. The tidal forcing from Sgr can produce changes in both guiding radius ($\Delta R_g$) and orbital eccentricity, as quantified by the maximum radial excursion, $\Delta R_{\max }$. These changes follow a quadrupole-like pattern across the face of the disc, with amplitude increasing with Galactocentric radius. We next examine a collisionless N-body simulation of a Sgr-like satellite interacting with a MW-like galaxy and find that Sgr's influence in the outer disc dominates over the secular evolution of orbits between disc passages. Finally, we use the same simulation to explore possible observable signatures of Sgr-induced migration by painting the simulation with different age stellar populations. We find that following Sgr disc passages, the migration it induces manifests within an annulus as an approximate quadrupole in azimuthal metallicity variations (${\delta }_{[Fe/H]}$), along with systematic variations in orbital eccentricity, $\Delta R_{\max }$. These systematic variations can persist for several rotational periods. We conclude that this combination of signatures may be used to distinguish between the different migration mechanisms shaping the chemical abundance patterns of the Milky Way's thin disc.

17 pages, 13 figures, submitted to MNRAS

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• Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars
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• The metallicity distribution in the core of the Sagittarus dwarf spheroidal: minimising the metallicity biases
• Empirical derivation of the metallicity evolution with time and radius using TNG50 Milky Way/Andromeda analogues
• The Non-Axisymmetric Influence: Radius and Angle-Dependent Trends in a Barred Galaxy
• Constraints on the history of Galactic spiral arms revealed by Gaia GSP-Spec alpha-elements
• Effects of secular growth and mergers on the evolution of metallicity gradients and azimuthal variations in a Milky Way-like galaxy
• Probing the origins. I. Generalised Additive Model inference of birth radii for Milky Way stars in the solar vicinity
• The Milky Way in context: The formation of galactic discs and chemical sequences from a cosmological perspective
• Metal-rich stellar counterpart of the Radcliffe Wave and the 3D chemical footprints of the Milky Way spiral arms
• Tidally-induced radial migration waves in LMC-like galaxies
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