The influence of Sagittarius and the Large Magellanic Cloud on the stellar disc of the Milky Way Galaxy

Abstract

We present N-body simulations of a Sagittarius-like dwarf spheroidal galaxy (Sgr) that follow its orbit about the Milky Way (MW) since its first crossing of the Galaxy's virial radius to the present day. As Sgr orbits around the MW, it excites vertical oscillations, corrugating and flaring the Galactic stellar disc. These responses can be understood by a two-phase picture in which the interaction is first dominated by torques from the wake excited by Sgr in the MW dark halo before transitioning to tides from Sgr's direct impact on the disc at late times. We show for the first time that a massive Sgr model simultaneously reproduces the locations and motions of arc-like over densities, such as the Monoceros Ring and the Triangulum Andromeda stellar clouds, that have been observed at the extremities of the disc, while also satisfying the solar neighbourhood constraints on the vertical structure and streaming motions of the disc. In additional simulations, we include the Large Magellanic Cloud (LMC) self consistently with Sgr. The LMC introduces coupling through constructive and destructive interference, but no new corrugations. In our models, the excitation of the current structure of the outer disk can be traced to interactions as far back as 6-7 Gyr ago (corresponding to z 1). Given the apparently quiescent accretion history of the MW over this timescale, this places Sgr as the main culprit behind the vertical oscillations of the disc and the last major accretion event for the Galaxy with the capacity to modulate its chemodynamical structure.

A Map of the Local Velocity Substructure in the Milky Way Disk

“…Although there might be other mechanisms for creating density and velocity substructure in the disk (Debattista 2014;Faure et al 2014;Monari et al 2015Monari et al , 2016, the observed oscillations are roughly consistent with simulations of the disk's response to a large (> 10 9 M ) satellite or dark subhalo passing near, or through, the disk (Kazantzidis et al 2008, Younger et al 2008, Minchev et al 2009, Purcell et al 2011, Gómez et al 2013, Widrow et al 2014, Laporte et al 2016. Corrugations have also been observed in HI gas and young stellar populations in the Milky Way (Spicker & Feitzinger 1986;Levine et al 2006), and in external galaxies (Matthews & Uson 2008a,b).…”

Gaia Reveals a Metal-rich, in situ Component of the Local Stellar Halo

“…Idealized simulations show that including density inhomogeneities in the gaseous disk heats up stellar disks (Struck & Elmegreen 2017), as does allowing for interactions with massive satellites (Laporte et al 2016). Such conditions were common at early cosmic times in the Latte simulation analyzed here.…”

Distribution functions for resonantly trapped orbits in the Galactic disc

“…It will also be mandatory to move away from the epicyclic approximation (McGill & Binney 1990;Sanders & Binney 2015). Once this will be done, in the absence of strong resonance overlaps, a complete dynamical model of the presentday Milky Way disc could then in principle finally be built by applying, on top of the trapped distribution function near the main resonances of each perturber, our previous Eulerian treatment of perturbations (Monari et al 2016a) for the other perturbers, even including vertical perturbations and "bending" modes of the disc (Widrow et al 2014;Xu et al 2015;Laporte et al 2016). …”