Accretion of the Magellanic System Onto the Galaxy

Abstract

Our Galaxy is surrounded by a large family of dwarf galaxies of which the most massive are the Large and Small Magellanic Clouds (LMC and SMC). Recent evidence suggests that systems with the mass of the Local Group accrete galaxies in smaller groups rather than individually. If so, at least some of the Galaxy's dwarfs may have fallen in with the LMC and SMC, and were formed as part of the Magellanic system in the nearby universe. We use the latest measurements of the proper motions of the LMC and SMC and a multicomponent model of the Galactic potential to explore the evolution of these galaxy configurations under the assumption that the Magellanic system may once have contained a number of bound dwarf galaxies. We compare our results to the available kinematic data for the local dwarf galaxies, and examine whether this model can account for recently discovered stellar streams and the planar distribution of Milky Way satellites. We find that in situations where the LMC and SMC are bound to the Milky Way, the kinematics of Draco, Sculptor, Sextans, Ursa Minor and the Sagittarius Stream are consistent with having fallen in along with the Magellanic system. These dwarfs, if so associated, will likely have been close to the tidal radius of the LMC originally and are unlikely to have affected each other throughout the orbit. However there are clear cases, such as Carina and Leo I, that cannot be explained this way.

Star formation sustained by gas accretion

“…Using a high-resolution dark-matter simulation of the local group, Libeskind et al (2011) concluded that the satellites of both MW and M31 were accreted anisotropically onto their haloes, entering the virial radius from a specific direction with respect to the large-scale structure. These conclusions are confirmed in other simulations of M31 dwarfs (Goerdt and Burkert 2013;Sadoun et al 2013), MW dwarfs (Nichols et al 2011;Lovell et al 2011), and in observations of dwarfs around NGC 3109 (Bellazzini et al 2013).…”

On the Hot Gas Content of the Milky Way Halo

“…The head-tail structure of high velocity clouds is another observation best explained in the context of a confining corona (Putman et al 2011). A separate argument for the existence of such a medium is the lack of detected HI in most dwarf spheroidal galaxies within 270 kpc of the Milky Way (Grcevich & Putman 2009) -a result that is naturally explained by ram pressure stripping by a ∼ 10 −4 cm −3 hot medium at ∼ 70 kpc (see also Moore & Davis 1994;Lin & Faber 1983;Nichols et al 2011).…”

An Ultra-Faint Galaxy Candidate Discovered in Early Data From the Magellanic Satellites Survey

“…For decades authors have speculated that some of the smaller Milky Way satellites may have originated with the Large and Small Magellanic Clouds (LMC, SMC; e.g., Lynden-Bell 1976;D'Onghia & Lake 2008;Nichols et al 2011;Sales et al 2011). The recent discovery of more than 20 ultra-faint ( M 8 V ) galaxy candidates by wide-area optical surveys, including the Dark Energy Survey (DES; Bechtol et al 2015;Drlica-Wagner et al 2015;Kim & Jerjen 2015;Koposov et al 2015a), the Survey of the MAgellanic Stellar History (SMASH ;Martin et al 2015), Pan-STARRS (Laevens et al 2015a(Laevens et al , 2015b, and VST ATLAS (Torrealba et al 2016a(Torrealba et al , 2016b, has renewed interest in identifying faint galactic companions of the Magellanic Clouds.…”