The Role of Dwarf Galaxy Interactions in Shaping the Magellanic System
  and Implications for Magellanic Irregulars
  We present a novel pair of numerical models of the interaction history
between the Large and Small Magellanic Clouds (LMC and SMC, respectively) and
our Milky Way (MW) in light of recent high precision proper motions
(Kallivayalil et al. 2006a,b). Given the new velocities, cosmological
simulations of structure formation favor a scenario where the Magellanic Clouds
(MCs) are currently on their first infall towards our Galaxy (Boylan-Kolchin et
al. 2011, Busha et al. 2011). We illustrate here that the observed irregular
morphology and internal kinematics of the MCs (in gas and stars) are naturally
explained by interactions between the LMC and SMC, rather than gravitational
interactions with the MW. This picture further supports a first infall scenario
(Besla et a. 2007). In particular, we demonstrate that the Magellanic Stream, a
band of HI gas trailing behind the MCs 150 degrees across the sky, can be
accounted for by the action of LMC tides on the SMC before the system was
accreted by the MW. We further demonstrate that the off-center, warped stellar
bar of the LMC and its one-armed spiral, can be naturally explained by a recent
direct collision with the SMC. Such structures are key morphological
characteristics of a class of galaxies referred to as Magellanic Irregulars (de
Vaucouleurs & Freeman 1972), the majority of which are not associated with
massive spiral galaxies. We infer that dwarf-dwarf galaxy interactions are
important drivers for the morphological evolution of Magellanic Irregulars and
can dramatically affect the efficiency of baryon removal from dwarf galaxies
via the formation of extended tidal bridges and tails. Such interactions are
important not only for the evolution of dwarf galaxies but also have direct
consequences for the buildup of baryons in our own MW, as LMC-mass systems are
believed to be the dominant building blocks of MW-type halos.
