On the Effect of the Large Magellanic Cloud on the Orbital Poles of Milky Way Satellite Galaxies

Abstract

The reflex motion and distortion of the Milky Way (MW) halo caused by the infall of a massive Large Magellanic Cloud (LMC) was shown to result in an excess of orbital poles of dark matter halo particles towards the LMC orbital pole. This was suggested to help explain the observed preference of MW satellite galaxies to co-orbit along the Vast Polar Structure (VPOS), the MW's satellite plane. We test this idea by correcting the positions and velocities of the MW satellites for the Galactocentric-distancedependent shifts inferred from a LMC-infall simulation. While this should substantially reduce the observed clustering of orbital poles if it were mainly caused by the LMC, we instead find that the strong clustering remains preserved. We confirm the initial study's result with our own simulation of an MW-LMC-like interaction, and use it to identify two reasons why this scenario is unable to explain the VPOS: (1) the orbital pole enhancement is very mild (∼ 10%) compared to the substantial observed enhancement (∼ 300%), and (2) it is very sensitive to the specific angular momenta of the simulation particles, with higher angular momentum particles being affected the least. Particles in simulated dark matter halos tend to follow more radial orbits (lower angular momentum), so their orbital poles are more easily affected by small offsets in position and velocity caused by an LMC infall than objects with more tangential velocity (higher angular momentum), such as the observed dwarf galaxies surrounding the MW. The origin of the VPOS thus remains unexplained.

Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies

“…Previous work has found that the MW dSphs share a common orientation and that it may be related to the Vast Polar Orbital structure (Sanders & Evans 2017). The Vast Polar Orbital structure and orbital poles alignment may be caused by the LMC (Garavito-Camargo et al 2021) but Pawlowski et al (2021) show the magnitude of the LMC perturbation is to small to fully explain the Vast Polar Orbital structure. Overall, we find excellent agreement between our results and other Gaia EDR3 proper motion results 3 (Mc-Connachie & Venn 2020b; Li et al 2021;Martínez-García et al 2021;Vitral 2021;Battaglia et al 2022;Qi et al 2022).…”

Constraining the Milky Way halo kinematics via its Linear Response to the Large Magellanic Cloud

“…But, as mentioned above, the actual global response of the DM halo (and, subsequently, of the stellar halo) is more subtle than that, and depends on the underlying distribution of DM in phase-space, as studied by, e.g., Laporte et al (2018); Garavito-Camargo et al (2019); Garavito-Camargo et al (2021a); Tamfal et al (2021). It has for instance been shown that the LMC could induce an overdensity in the orbital poles of particles moving through the halo (Garavito-Camargo et al 2021b), although it has been subsequently shown that the effect was only present for particles with low specific angular momentum (Pawlowski et al 2021).…”