The role of dwarf galaxy interactions in shaping the Magellanic System and implications for Magellanic Irregulars

Abstract

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 from the Hubble Space Telescope. Given the updated velocities, cosmological simulations of hierarchical structure formation favour a scenario where the Magellanic Clouds (MCs) are currently on their first infall towards our Galaxy. We illustrate here that the observed irregular morphology and internal kinematics of the Magellanic System (in gas and stars) are naturally explained by interactions between the LMC and SMC, rather than gravitational interactions with the MW. These conclusions provide further support that the MCs are completing their first infall to our system. In particular, we demonstrate that the Magellanic Stream, a band of H i gas trailing behind the Clouds 150° 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‐centre, warped stellar bar of the LMC, and its one‐armed spiral can be naturally explained by a recent direct collision with its lower mass companion, the SMC. Such structures are key morphological characteristics of a class of galaxies referred to as Magellanic Irregulars, 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 not only important for the evolution of dwarf galaxies but also have direct consequences for the build‐up of baryons in our own MW, as LMC‐mass systems are believed to be the dominant building blocks of MW‐type haloes.

The MAGellanic Inter-Cloud (MAGIC) project – II. Slicing up the Bridge

“…Unfortunately, at our current CMD-age resolution these two options are degenerate. Based on their proper motions, the clouds likely interacted just ∼200 Myr ago (Besla et al 2012) which is comparable to the recent star formation burst (see Fig. 7).…”

“…Noël et al 2013b). Secondly, due to their mutual association over the past few Gyr (as determined from their proper motions: Kallivayalil, van der Marel & Alcock 2006;Besla et al 2007Besla et al , 2012Piatek, Pryor & Olszewski 2008;Costa et al 2011;Kallivayalil et al 2013;van der Marel & Kallivayalil 2014;Cioni et al 2014;and numerical simulations: Bekki 2011;Diaz & Bekki 2012;Besla, Hernquist & Loeb 2013). Thirdly, because of their significant gas reservoirs (e.g.…”

The Properties of the Magellanic Bridge Based on OGLE IV RR Lyrae Variables

“…Proper motion and internal kinematics suggest that the MB likely resulted from a recent direct collision of the two galaxies (Kallivayalil et al 2013;Besla et al 2012;Diaz & Bekki 2012). Such an interaction is thought to have triggered star formation in the MB, as pointed out by Grondin, Demers & Kunkel (1992); Mizuno et al (2006); Skowron et al (2014); Chen et al (2014).…”

A Hubble Space Telescope Study of the Enigmatic Milky Way Halo Globular Cluster Crater*

“…Based on its position in the Galaxy, Crater (L MS , B MS , V GSR =+80.6943, −5.87460, +150 km s −1 , where "MS" denotes the Magellanic Stream coordinate system) is well-matched to the location of tidal debris from the Magellanic Stream as predicted by the models of Besla et al (2012). Furthermore, Crater's heliocentric velocity of~+150 km s −1 (Kirby et al 2015) is consistent with the measured gas velocity of the Magellanic Stream of 100-200 km s −1 (Nidever et al 2010).…”