Constraining the Milky Way halo potential with the GD-1 stellar stream

Abstract

We use ESA/Gaia astrometry together with SEGUE and LAMOST measurements of the GD-1 stellar stream to explore the improvement on the Galactic gravitational potential that these new data provide. Assuming a realistic universal model for the dark matter halo together with reasonable models of the baryonic components, we find that the orbital solutions for GD-1 require the circular velocity at the Solar radius to be V_circ(R_⊙) =244± 4{ km s^{-1}}, and also that the density flattening of the dark halo is q_{ρ }=0.82^{+0.25}_{-0.13}. The corresponding Galactic mass within 20{ kpc} was estimated to be M_MW(< 20{ kpc})=2.5± 0.2 × 10^{11} { M_⊙}. Moreover, Gaia's excellent proper motions also allowed us to constrain the velocity dispersion of the GD-1 stream in the direction tangential to the line of sight to be < 2.30{ km s^{-1}} (95 per cent confidence limit), confirming the extremely cold dynamical nature of this system.