Substructure at High Speed II: The Local Escape Velocity and Milky Way Mass with Gaia DR2

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 (2021), 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 second data release of Gaia and find that a model with at least two components is preferred. Based on a fit with three bound components to account for the disk, relaxed halo, and the Gaia Sausage, we find the escape velocity of the Milky Way at the solar position to be $v_{\mathrm{esc}}=484.6_{-7.4}^{+17.8}$ km/s. Assuming a Navarro-Frenck-White dark matter profile, and taken in conjunction with a recent measurement of the circular velocity at the solar position of $v_c=230\pm 10$ km/s, we find a Milky Way concentration of $c_{200}=13.8_{-4.3}^{+6.0}$ and a mass of $M_{200}=7.0_{-1.2}^{+1.9}\times 10^{11}{M}_{\odot }$, which is considerably lighter than previous measurements.

10+7 pages, 7+7 figures

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• Reacceleration of Galactic Cosmic Rays Beyond the Knee at the Termination Shock of a Cosmic-Ray-Driven Galactic Wind
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• Gusts in the Headwind: Uncertainties in Direct Dark Matter Detection
• Substructure at High Speed I: Inferring the Escape Velocity in the Presence of Kinematic Substructure
• The outskirts of M33: Tidally induced distortions versus signatures of gas accretion
• Milky Way Mass Through Escape Velocity Curve from LAMOST K Giants
• Information-theoretic astrophysical uncertainties in the effective theory of dark matter direct detection
• Observing the Migdal effect from nuclear recoils of neutral particles with liquid xenon and argon detectors