The Influence of Sagittarius and the Large Magellanic Cloud on the Milky Way Galaxy

TL;DR

This study uses N-body simulations to show how the Sagittarius dwarf galaxy and the Large Magellanic Cloud have shaped the Milky Way's disc, explaining observed stellar structures and oscillations over billions of years.

Contribution

It demonstrates that a massive Sagittarius model can reproduce observed stellar over densities and disc oscillations, highlighting its role as the last major accretion event influencing the Milky Way.

Findings

Sagittarius excites vertical oscillations in the Milky Way disc.

The model reproduces observed structures like the Monoceros Ring.

Interactions over 6-7 Gyr ago shape the current disc features.

Abstract

We present N-body simulations of a Sagittarius-like dwarf spheroidal galaxy (Sgr) that follow its orbit about the Milky Way (MW) since its first crossing of the Galaxy's virial radius to the present day. As Sgr orbits around the MW, it excites vertical oscillations, corrugating and flaring the Galactic stellar disc. These responses can be understood by a two-phase picture in which the interaction is first dominated by torques from the wake excited by Sgr in the MW dark halo before transitioning to tides from Sgr's direct impact on the disc at late times. We show for the first time that a massive Sgr model simultaneously reproduces the locations and motions of arc-like over densities, such as the Monoceros Ring and the Triangulum Andromeda stellar clouds, that have been observed at the extremities of the disc, while also satisfying the solar neighbourhood constraints on the vertical structure and streaming motions of the disc. In additional simulations, we include the Large Magellanic Cloud (LMC) self consistently with Sgr. The LMC introduces coupling through constructive and destructive interference, but no new corrugations. In our models, the excitation of the current structure of the outer disk can be traced to interactions as far back as 6-7 Gyr ago (corresponding to $z\leq1$). Given the apparently quiescent accretion history of the MW over this timescale, this places Sgr as the main culprit behind the vertical oscillations of the disc and the last major accretion event for the Galaxy with the capacity to modulate its chemodynamical structure.