IAUS379: Dynamical Masses of Local Group Galaxies

Recent panoramic maps of the Magellanic system have revealed a wealth of low-surface-brightness stellar substructures surrounding both the Large and Small Magellanic Clouds (LMC/SMC); clear evidence of tidal interactions between the two Clouds, as well as with the Milky Way. However, the interaction history of the Magellanic system beyond the most recent LMC/SMC close passage remains poorly constrained. In order to shed light on this issue, we have instigated a large-scale spectroscopic follow-up of stars in low-density features extending to distances beyond 20 degrees from the Clouds’ centres. We use a combination of Gaia astrometry and spectroscopically-derived radial velocities, obtained with 2dF+AAOmega on the Anglo-Australian Telescope, to determine 3D kinematics for thousands of stars in these features and the extended outer disks of the two Clouds. In this talk, I will discuss new results focussed on the southern outskirts of the LMC. Several substructures in this region, including claw-like features extending from the southern LMC disk, and a long arm-like substructure wrapping around the southern LMC outskirts toward the eastern SMC disk, are found to be predominantly composed of perturbed LMC disk material. All substructures show significant perturbations from equilibrium disk kinematics, with one claw-like feature displaying out-of-plane velocities exceeding 60 km/s and apparent counter-rotation relative to the LMC’s disk. Such complex features plausibly require multiple previous interactions with the SMC to fully explain the observed dynamical properties. This demonstrates the efficacy of our data as a benchmark for assessing dynamical models to disentangle the origins of Magellanic substructures, the masses of the two Clouds, and the evolution of the Magellanic system. I will also briefly discuss new efforts to conduct analogous kinematic mapping of M33 and its outskirts, which aim to similarly understand the evolution of this massive dwarf galaxy.