I will present a new numerical model of the evolution of the Milky Way’s largest satellite galaxies, the Large and Small Magellanic Clouds (LMC/SMC), in which their current internal structure and kinematics and large-scale gas morphology are dictated by their mutual tidal interactions, rather than interactions with the Milky Way.  This picture is consistent with the recent HST proper motions of the LMC (Kallivayalil et al. 2006) – using cosmologically motivated models for the Milky Way, these new proper motions imply that the Clouds have not made multiple passages about the Milky Way.

In particular, the LMC’s peculiar off-center bar and one-armed spiral morphology is a natural by-product of a recent direct collision with the SMC.  This scenario may shed light on the dynamical state of a class of dwarf galaxies known as Magellanic Irregulars (de Vaucouleurs & Freeman 1972), which, like the LMC, are asymmetric spirals with off-center bars, but are rarely associated with massive spirals.

As a result of its collision with the LMC, the simulated SMC is left in a highly disturbed state where its older stellar population does not display a pronounced rotation curve, as observed. The SMC may thus represent an object in transition from a dwarf Irregular galaxy to a dwarf Spheroidal.  This process is expected to occur ubiquitously in small groups of low mass galaxies and may represent a generic mode of dwarf galaxy evolution that is independent of proximity to a massive host.