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.

arXiv comment17+13 pages, 13+14 figures

References in corpus (44)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• The Aquarius Project: the subhalos of galactic halos
• galpy: A Python Library for Galactic Dynamics
• The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• GIZMO: A New Class of Accurate, Mesh-Free Hydrodynamic Simulation Methods
• FIRE-2 Simulations: Physics versus Numerics in Galaxy Formation
• Co-formation of the Galactic disc and the stellar halo
• The Field of Streams: Sagittarius and its Siblings
• Clumps and streams in the local dark matter distribution
• The RAVE Survey: Constraining the Local Galactic Escape Speed
• Reconciling dwarf galaxies with LCDM cosmology: Simulating a realistic population of satellites around a Milky Way-mass galaxy
• Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes
• Debris streams in the solar neighbourhood as relicts from the formation of the Milky Way
• The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time
• A Faint New Milky Way Satellite in Bootes
• Streams, substructures and the early history of the Milky Way
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• A Curious New Milky Way Satellite in Ursa Major
• The RAVE survey: the Galactic escape speed and the mass of the Milky Way
• The Formation and Survival of Discs in a Lambda-CDM Universe
• An Orphan in the "Field of Streams"
• The Sausage Globular Clusters
• Segue 2: The Least Massive Galaxy
• Apocenter Pile-Up: Origin of the Stellar Halo Density Break
• The escape speed curve of the Galaxy obtained from Gaia DR2 implies a heavy Milky Way
• Halo Substructure in the SDSS-Gaia Catalogue : Streams and Clumps
• The local high velocity tail and the Galactic escape speed
• Nearest Neighbor: The Low-Mass Milky Way Satellite Tucana III
• Inferred Evidence For Dark Matter Kinematic Substructure with SDSS-Gaia
• The Halo's Ancient Metal-Rich Progenitor Revealed with BHB Stars
• On the Run: mapping the escape speed across the Galaxy with SDSS
• The Origin of Segue 1
• Reconciling observed and simulated stellar halo masses
• Under the Firelight: Stellar Tracers of the Local Dark Matter Velocity Distribution in the Milky Way
• Old, Metal-Poor Extreme Velocity Stars in the Solar Neighborhood
• 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
• Chasing Accreted Structures within Gaia DR2 using Deep Learning
• 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

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• 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