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The shape of the inner Milky Way halo from observations of the Pal 5 and GD-1 stellar streams

2 Pith papers cite this work. Polarity classification is still indexing.

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abstract

We constrain the shape of the Milky Way's halo by dynamical modeling of the observed phase-space tracks of the Pal 5 and GD-1 tidal streams. We find that the only information about the potential gleaned from the tracks of these streams are precise measurements of the shape of the gravitational potential---the ratio of vertical to radial acceleration---at the location of the streams, with weaker constraints on the radial and vertical accelerations separately. The latter will improve significantly with precise proper-motion measurements from Gaia. We measure that the overall potential flattening is 0.95 +/- 0.04 at the location of GD-1 ([R,z] ~ [12.5,6.7] kpc) and 0.94 +/- 0.05 at the position of Pal 5 ([R,z] ~ [8.4,16.8] kpc). Combined with constraints on the force field near the Galactic disk, we determine that the axis ratio of the dark-matter halo's density distribution is 1.05 +/- 0.14 within the inner 20 kpc, with a hint that the halo becomes more flattened near the edge of this volume. The halo mass within 20 kpc is 1.1 +/- 0.1 x 10^{11} M_sun. A dark-matter halo this close to spherical is in tension with the predictions from numerical simulations of the formation of dark-matter halos.

fields

astro-ph.GA 2

years

2026 2

verdicts

UNVERDICTED 2

representative citing papers

Bar-induced deflection of open cluster tidal tails

astro-ph.GA · 2026-06-04 · unverdicted · novelty 5.0

Test-particle simulations show that Galactic bar pattern speed systematically deflects open-cluster tidal tail orientations, with NGC 2632 and Hyades tails disfavouring moderate speeds.

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