Extent of a smooth stellar halo component in the Milky Way’s outer halo

Ascertain the extent to which the Milky Way possesses a smooth stellar halo component at Galactocentric distances greater than approximately 50 kpc, rather than being predominantly composed of substructure and disequilibrium features induced by interactions such as the Large Magellanic Cloud infall.

Background

Many dynamical analyses of the Milky Way assume that the stellar halo can be treated as a smooth, equilibrium component, which is crucial for methods that infer the Galaxy’s mass distribution. However, in the outer halo (beyond ~50 kpc), the recent infall of the Large Magellanic Cloud and the presence of substantial substructure (e.g., Sagittarius stream, Magellanic debris, overdensities) may violate these assumptions.

The paper’s results highlight pronounced disequilibrium signatures (e.g., a growing reflex motion with distance), raising the question of whether a sufficiently smooth stellar halo exists at these large radii to justify equilibrium modeling. Determining the degree of smoothness is therefore essential for robust dynamical interpretations of the outer halo.