Dynamics of the Magellanic Clouds in a LCDM Universe

TL;DR

This study uses cosmological simulations to analyze the orbital history of the Magellanic Clouds, suggesting the LMC was recently accreted and is on its first orbit around the Milky Way, with implications for the galaxy's mass.

Contribution

It provides a cosmological context for the Magellanic Clouds' orbits, indicating recent accretion and constraining the Milky Way's halo mass based on orbital dynamics.

Findings

LMC and SMC-mass objects are common in MW-like halos.

High LMC velocity is consistent with a MW halo mass of at least 2 x 10^12 Msun.

LMC was likely accreted within the last four Gyr and is on its first pericentric passage.

Abstract

We examine Milky Way-Magellanic Cloud systems selected from the Millennium-II Simulation in order to place the orbits of the Magellanic Clouds in a cosmological context. Our analysis shows that satellites massive enough to be LMC analogs are typically accreted at late times. Moreover, those that are accreted at early times and survive to the present have orbital properties that are discrepant with those observed for the LMC. The high velocity of the LMC, coupled with the dearth of unbound orbits seen in the simulation, argues that the mass of the MW's halo is unlikely to be less than 2 x 10^12 Msun. This conclusion is further supported by statistics of halos hosting satellites with masses, velocities, and separations comparable to those of the LMC. We further show that: (1) LMC and SMC-mass objects are not particularly uncommon in MW-mass halos; (2) the apparently high angular momentum of the LMC is not cosmologically unusual; and (3) it is rare for a MW halo to host a LMC-SMC binary system at z=0, but high speed binary pairs accreted at late times are possible. Based on these results, we conclude that the LMC was accreted within the past four Gyr and is currently making its first pericentric passage about the MW.