Modeling the recent interactions between the Magellanic Clouds and Milky Way

TL;DR

This study tackles reconstructing the recent orbital history of the Magellanic Clouds by combining high-resolution N-body simulations with a genetic algorithm to infer initial conditions ~2.5 Gyr ago that reproduce present-day MC positions, velocities, and substructures. The authors demonstrate two close MC passages at about 940 Myr and 140 Myr ago and reproduce key features such as an LMC disc warp, a ring-like overdensity, and the northern LMC stream, while also predicting SMC tidal expansion and eastern-distance bimodality; some observed features (LMC hooks, SMCNOD) remain unmatched, indicating missing physics or earlier interactions. The work emphasizes the necessity of including MW tides and complex three-body dynamics when modeling the MC system and provides a framework for connecting orbital histories to observable substructures. The findings offer insights into the dynamical state and past interactions of the Magellanic System and set the stage for future, higher-resolution simulations and deeper observational tests, including the predicted vertical oscillations in the LMC disc.

Abstract

The Large and Small Magellanic Clouds (LMC and SMC, respectively) are the largest satellite galaxies of the Milky Way (MW) and their interactions with each other have given rise to multiple stellar substructures in their periphery as well as the gaseous Magellanic Stream. To better understand the origin of the stellar substructures and constrain their past orbit, we model the past 2.5 Gyr of the interactions between the MW and the LMC and SMC using N-body simulations. Due to the strong interactions, analytical orbit integrations are insufficient to analyze the past galaxy orbits accurately. Therefore, we use a genetic algorithm in combination with N-body simulations to determine the LMC and SMC initial positions and velocities 2.5 Gyr ago that result in the Magellanic Clouds (MCs) arriving near their observed locations and velocities at the current time. After running ~8,000 simulations, our best matching model includes two close interactions between the MCs (940 Myr and 140 Myr ago) and reproduces some observed features of the MCs, including the LMC disc warp, a ring-shaped overdensity in the LMC, the tidal expansion of the SMC, and a greater distance dispersion on the eastern side of the SMC. The LMC disc warp is caused by the most recent interaction with the SMC, which occurred ~140 Myr before the present. The interaction causes global ripples in the LMC disc with a mean amplitude of 1.3 kpc.

Figures (28)

• Figure 1: Color magnitude diagram of Gaia EDR3 MC stars. The black boundary shows the cuts we use for MC red clump and red giant branch stars.
• Figure 2: Density map of Gaia MC giant stars. The black line shows the selection we used on the map of the stars on Magellenic Stream coordinates $L_{MS}$ and $B_{MS}$.
• Figure 3: Maps of the observed Gaia and SDSS MC data. left: Number of stars, center left: mean proper motion in the $L_{\rm MS}$ direction, center right: mean proper motion in the $B_{\rm MS}$ direction, and right mean line-of-sight velocity.
• Figure 4: Diagram of the coordinates we define for our two-galaxy simulations. Top: projection onto the $x-y$ plane. Bottom: projection onto the plane perpendicular to the $x-y$ plane that includes the initial location of the SMC center and point P.
• Figure 5: The LMC and SMC at the end of a two-galaxy simulation.