The Mass of the Large Magellanic Cloud from the Three-Dimensional Kinematics of its Globular Clusters

Abstract

We estimate the mass of the Large Magellanic Cloud (LMC) using the kinematics of 30 LMC globular clusters (GCs). We combine proper motions (PMs) measured with HST, Gaia, or a combination of the two, from a recent study by Bennet et al. (2022) with literature line-of-sight velocities (LOSVs) to give 3 components of motion. With these, we derive a 3D velocity dispersion anisotropy \(\beta = -0.72 ^{+0.62} _{-1.07}\), consistent with the GCs forming a flattened system with significant azimuthal motion. We then apply a tracer mass estimator and measure an enclosed mass \(M (<13.2 \mathrm{kpc})= 2.66^{+0.42} _{-0.36} \times 10^{10} \mathrm{M}_\odot\). This is broadly consistent with results from previous studies of the LOSVs of GCs and other luminous tracers. Assuming a cosmologically-constrained NFW distribution for the dark matter, this implies a virial mass \(M_\mathrm{virial} = 1.80^{+1.05} _{-0.54} \times 10^{11} \mathrm{M}_\odot\). Despite being an extrapolation by almost an order of magnitude in radius, this result is consistent with published estimates from other methods that are directly sensitive to the LMC's total mass. Our results support the conclusion that the LMC is approximately 17\(^{+10}_{-6}\)% of the Milky Way's mass, making it a significant contributor to the Local Group (LG) potential.