The Magellanic Edges Survey II. Formation of the LMC's northern arm

The highly-substructured outskirts of the Magellanic Clouds provide ideal locations for studying the complex interaction history between both Clouds and the Milky Way (MW). In this paper, we investigate the origin of a >20$^\circ$ long arm-like feature in the northern outskirts of the Large Magellanic Cloud (LMC) using data from the Magellanic Edges Survey (MagES) and Gaia EDR3. We study the metallicity, structure, and kinematics of the arm, finding it has a similar geometry and [Fe/H] abundance to the nearby outer LMC disk, and is likely comprised of perturbed disk material. Whilst the azimuthal velocity and velocity dispersions along the arm are consistent with those in the outer LMC, the in-plane radial velocity and out-of-plane vertical velocity are significantly perturbed from equilibrium disk kinematics. Comparison with a new suite of dynamical models of the Magellanic/MW system reveals the tidal force of the MW during the LMC's infall is primarily responsible for the formation of the arm. Close LMC/SMC interactions within the past Gyr, particularly the SMC's pericentric passage ~150 Myr ago and a recent SMC crossing of the LMC disk plane ~400 Myr ago, do not perturb stars that today comprise the arm, and are instead likely responsible for structures in the western LMC disk. Nonetheless, historical interactions with the SMC prior to ~1 Gyr ago may be required to explain some of the observed kinematic properties of the arm, in particular a strongly negative in-plane radial velocity.