The escape speed curve of the Galaxy obtained from Gaia DR2 implies a heavy Milky Way

Abstract

We measure the escape speed curve of the Milky Way based on the analysis of the velocity distribution of 2850 counter-rotating halo stars from the Gaia Data Release 2. The distances were estimated through the StarHorse code, and only stars with distance errors smaller than 10% were used in the study. The escape speed curve is measured at Galactocentric radii ranging from 5 kpc to 10.5 kpc. The local Galactic escape at the Sun's position is estimated to be v_e(r_⊙) = 580 ± 63 km s^-1, and it rises towards the Galactic centre. Defined as the minimum speed required to reach three virial radii, our estimate of the escape speed as a function of radius implies for a Navarro-Frenk-White profile and local circular velocity of 240 km s^-1 a dark matter mass M₂₀₀ = 1.28_-0.50^+0.68 × 10¹² M_⊙ and a high concentration c₂₀₀ = 11.09_-1.79^+2.94. Assuming the mass-concentration relation of ΛCDM, we obtain M₂₀₀ = 1.55_-0.51^+0.64 × 10¹² M_⊙ and c₂₀₀ = 7.93_-0.27^+0.33 for a local circular velocity of 228 km s^-1.