Substructure at High Speed I: Inferring the Escape Velocity in the Presence of Kinematic Substructure

Abstract

The local escape velocity provides valuable inputs to the mass profile of the Galaxy, and requires understanding the tail of the stellar speed distribution. Following Leonard $\&$ Tremaine (1990), various works have since modeled the tail of the stellar speed distribution as $\propto (v_{\mathrm{esc}}-v{)}^k$, where $v_{\mathrm{esc}}$ is the escape velocity, and $k$ is the slope of the distribution. In such studies, however, these two parameters were found to be largely degenerate and often a narrow prior is imposed on $k$ in order to constrain $v_{\mathrm{esc}}$. Furthermore, the validity of the power law form is likely to break down in the presence of multiple kinematic substructures. In this paper, we introduce a strategy that for the first time takes into account the presence of kinematic substructure. We model the tail of the velocity distribution as a sum of multiple power laws without imposing strong priors. Using mock data, we show the robustness of this method in the presence of kinematic structure that is similar to the recently-discovered Gaia Sausage. In a companion paper, we present the new measurement of the escape velocity and subsequently the mass of the Milky Way using Gaia DR2 data.

17+13 pages, 13+14 figures

References in corpus (12)

• galpy: A Python Library for Galactic Dynamics
• The RAVE Survey: Constraining the Local Galactic Escape Speed
• Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes
• The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• An Orphan in the "Field of Streams"
• Halo Substructure in the SDSS-Gaia Catalogue : Streams and Clumps
• The local high velocity tail and the Galactic escape speed
• The effects of dynamical substructure on Milky Way mass estimates from the high velocity tail of the local stellar halo
• Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V
• Determination of the escape velocity of the Milky Way using a proper motion selected halo sample
• Substructure at High Speed II: The Local Escape Velocity and Milky Way Mass with Gaia DR2

Cited by in corpus (5)

• Substructure at High Speed II: The Local Escape Velocity and Milky Way Mass with Gaia DR2
• Milky Way archaeology using RR Lyrae and type II Cepheids II. High velocity RR Lyrae stars, and mass of the Milky Way
• The Escape Velocity Profile of the Milky Way from Gaia DR3
• Milky Way Mass Through Escape Velocity Curve from LAMOST K Giants
• Information-theoretic astrophysical uncertainties in the effective theory of dark matter direct detection