"Skinny Milky Way, Please", says Sagittarius

TL;DR

This paper introduces a rapid, accurate method for modeling stellar tidal streams, applied to the Sagittarius stream, providing new insights into the Milky Way's mass distribution and supporting a lighter galaxy model.

Contribution

The authors develop a fast algorithm for generating realistic tidal stream models that incorporate the progenitor's gravity, enabling unbiased inference of the Galactic mass profile from stream data.

Findings

The method accurately reproduces stream features in mock data.

Applied to Sagittarius, it suggests a lighter Milky Way mass.

Results align with independent halo star and satellite galaxy studies.

Abstract

Motivated by recent observations of the Sagittarius stream, we devise a rapid algorithm to generate faithful representations of the centroids of stellar tidal streams formed in a disruption of a progenitor of an arbitrary mass in an arbitrary potential. Our method works by releasing swarms of test particles at the Lagrange points around the satellite and subsequently evolving them in a combined potential of the host and the progenitor. We stress that the action of the progenitor's gravity is crucial to making streams that look almost indistinguishable from the N-body realizations, as indeed ours do. The method is tested on mock stream data in three different Milky Way potentials with increasing complexity, and is shown to deliver unbiased inference on the Galactic mass distribution out to large radii. When applied to the observations of the Sagittarius stream, our model gives a natural explanation of the stream's apocentric distances and the differential orbital precession. We, therefore, provide a new independent measurement of the Galactic mass distribution beyond 50 kpc. The Sagittarius stream model favours a light Milky Way with the mass 4.1 +/- 0.4 x 10^11 M_sun at 100 kpc, which can be extrapolated to 5.6 +/- 1.2 x 10^11 M_sun at 200 kpc. Such a low mass for the Milky Way Galaxy is in good agreement with estimates from the kinematics of halo stars and from the satellite galaxies (once Leo I is removed from the sample). It entirely removes the "Too Big To Fail Problem".