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 nonaxisymmetric 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 Δ𝑅 𝑔 and orbital eccentricity, as quantified by the maximum radial excursion Δ𝑅 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 (𝛿 [Fe/H] ), along with systematic variations in orbital eccentricity, Δ𝑅 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.

The chemical signature of the Galactic spiral arms revealed by Gaia DR3

“…Chemo-dynamical evolution models should be adopted to interpret the impact of the spiral arms on chemical variations in the Galactic disc, and to understand how different mechanisms can influence the observed present-day chemical abundance patterns (e.g. Roškar et al 2012;Grand et al 2016;Minchev et al 2018;Spitoni et al 2019Spitoni et al , 2022aCarr et al 2022). Future works comparing observations from Gaia DR3 and groundbased surveys to sophisticated theoretical models will be able to provide further insights on the evolutionary processes that shaped the present-day appearance of the Milky Way's disc For the obtained sample, we calculated the Galactocentric coordinates R, ϕ, Z and the corresponding velocities V R , V ϕ , V Z following the same conventions and parameters adopted in Gaia Collaboration, Recio-Blanco et al (2022).…”

The Milky Way tomography with APOGEE: intrinsic density distribution and structure of mono-abundance populations

“…However, the youngest solar-abundance MAP, which should not have experienced much radial migration (Lian et al in preparation), also shows this behavior, which implies a possibly different origin of the flat radial density distribution in the inner Galaxy. For example, interactions between Sagittarius and the disk may result in significant radial mixing (Carr et al 2022).…”