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

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)_Φ= 0.8 and intermediate-to-major axis ratio (b/a)_Φ= 0.9, in good agreement with cosmological expectations.

5 pages, 5 figures. Accepted for publication in ApJ Letters. Minor changes to match published version

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