Constraints on the shape of the Milky Way dark matter halo from the Sagittarius stream

TL;DR

This paper models the Milky Way's dark matter halo using the Sagittarius stream, accounting for the Large Magellanic Cloud's influence, and constrains the halo's shape to align with cosmological expectations.

Contribution

It introduces a new halo model fitting the Sagittarius stream and incorporates LMC effects to better constrain the halo shape.

Findings

Halo is oblate with q_z = 0.9 within 10 kpc

Outer halo shape constrained to (c/a)_Φ = 0.8 and (b/a)_Φ = 0.9

LMC perturbations significantly affect stream modeling

Abstract

We propose a new model for the dark matter halo of the Milky Way that fits the properties of the stellar stream associated with the Sagittarius dwarf galaxy. Our dark halo is oblate with q_z = 0.9 for r < 10 kpc, and can be made to follow the Law & Majewski model at larger radii. However, we find that the dynamical perturbations induced by the Large Magellanic Cloud on the orbit of Sgr cannot be neglected when modeling its streams. When taken into account, this leads us to constrain the Galaxy's outer halo shape to have minor-to-major axis ratio (c/a)_\Phi = 0.8 and intermediate-to-major axis ratio (b/a)_\Phi = 0.9, in good agreement with cosmological expectations.