Substructure at High Speed. II. The Local Escape Velocity and Milky Way Mass with Gaia eDR3

Abstract

Measuring the escape velocity of the Milky Way is critical in obtaining the mass of the Milky Way, understanding the dark matter velocity distribution, and building the dark matter density profile. In Necib & Lin, we introduced a strategy to robustly measure the escape velocity. Our approach takes into account the presence of kinematic substructures by modeling the tail of the stellar distribution with multiple components, including the stellar halo and the debris flow called the Gaia Sausage (Enceladus). In doing so, we can test the robustness of the escape velocity measurement for different definitions of the "tail" of the velocity distribution and the consistency of the data with different underlying models. In this paper, we apply this method to the Gaia eDR3 data release and find that a model with two components is preferred, although results from a single-component fit are also consistent. Based on a fit to retrograde data with two bound components to account for the relaxed halo and the Gaia Sausage, we find the escape velocity of the Milky Way at the solar position to be v_(esc) = 445⁺²⁵₋₈ km s⁻¹. A fit with a single component to the same data gives v_(esc) = 472⁺¹⁷₋₁₂ km s⁻¹. Assuming a Navarro−Frenck−White dark matter profile, we find a Milky Way concentration of c₂₀₀ = 19⁺¹¹₋₇ and a mass of M₂₀₀ = 4.6^(+1.5)_(-0.8) x 10¹¹M⊙, which is considerably lighter than previous measurements.