Letter to the Editor

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

¹ Leibniz – Institut fuer Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: gmonari@aip.de
² Université de Strasbourg, Observatoire astronomique de Strasbourg, CNRS UMR 7550, 11 rue de l’Université, 67000 Strasbourg, France
³ Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
⁴ Leverhulme Trust Visiting Professor, University of Edinburgh, Edinburgh, UK

Received: 29 June 2018
Accepted: 5 July 2018

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.