Implications of the Milky Way travel velocity for dynamical mass estimates of the Local Group

Abstract

The total mass of the Local Group (LG) is a fundamental quantity that enables interpreting the orbits of its constituent galaxies and placing the LG in a cosmological context. One of the few methods that allows inferring the total mass directly is the "Timing Argument," which models the relative orbit of the Milky Way (MW) and M31 in equilibrium. The MW itself is not in equilibrium, a byproduct of its merger history including the recent pericentric passage of the LMC, and recent work has found that the MW disk is moving with a lower bound "travel velocity" of $\sim 32\mathrm{km}{\mathrm{s}}^{-1}$ with respect to the outer stellar halo. Previous Timing Argument measurements attempt to account for this non-equilibrium state, but have been restricted to theoretical predictions for the impact of the LMC specifically. In this paper, we quantify the impact of a travel velocity on recovered LG mass estimates using several different compilations of recent kinematic measurements of M31. We find that incorporating the measured value of the travel velocity lowers the inferred LG mass by 10--12\% compared to a static MW halo. Measurements of the travel velocity with more distant tracers could yield even larger values, which would further decrease the inferred LG mass. Therefore, the newly measured travel velocity directly implies a lower LG mass than from a model with a static MW halo and must be considered in future dynamical studies of the Local Volume.

14 pages, 3 figures; Published in ApJ; updated to match published version

References in corpus (27)

• Array Programming with NumPy
• The Gaia mission
• The M31 Velocity Vector. II. Radial Orbit Towards the Milky Way and Implied Local Group Mass
• The Gas Content and Stripping of Local Group Dwarf Galaxies
• The M31 Velocity Vector. I. Hubble Space Telescope Proper Motion Measurements
• Orbits of Massive Satellite Galaxies: I. A Close Look at the Large Magellanic Cloud and a New Orbital History for M33
• Quantifying the impact of the Large Magellanic Cloud on the structure of the Milky Way's dark matter halo using Basis Function Expansions
• M31 Transverse Velocity and Local Group Mass from Satellite Kinematics
• All-Sky Dynamical Response of the Galactic Halo to the Large Magellanic Cloud
• A dynamical model of the local cosmic expansion
• Detection of the Milky Way reflex motion due to the Large Magellanic Cloud infall
• Detection of the LMC-induced sloshing of the Galactic halo
• The mass of the Milky Way out to 100 kpc using halo stars
• Reflex motion in the Milky Way stellar halo resulting from the Large Magellanic Cloud infall
• Properties of HI discs in the Auriga cosmological simulations
• Balancing mass and momentum in the Local Group
• Quantifying the Stellar Halo's Response to the LMC's Infall with Spherical Harmonics
• A sub-2% Distance to M31 from Photometrically Homogeneous Near-Infrared Cepheid Period-Luminosity Relations Measured with the Hubble Space Telescope
• Milky Way total Mass derived by Rotation Curve and Globular Cluster kinematics from Gaia EDR3
• The Local Group Mass in the light of Gaia
• The proper motion of Andromeda from Gaia eDR3: confirming a nearly radial orbit
• The sum of the masses of the Milky Way and M31: a likelihood-free inference approach
• The SIBELIUS Project: E Pluribus Unum
• Constraining the mass of the Local Group
• Local Group timing argument and virial theorem mass estimators from cosmological simulations
• Local Group Analogs in $\Lambda$CDM cosmological simulations
• Metallicity distribution of the progenitor of the Giant Stellar Stream in the Andromeda Galaxy

Cited by in corpus (17)

• The effect of the LMC on the Milky Way system
• Structure, Kinematics, and Observability of the Large Magellanic Cloud's Dynamical Friction Wake in Cold vs. Fuzzy Dark Matter
• Evidence for a Massive Andromeda Galaxy Using Satellite Galaxy Proper Motions
• Constraining Dark Energy from Local Group dynamics
• The Local Group's mass: probably no more than the sum of its parts
• All-Sky Kinematics of the Distant Halo: The Reflex Response to the LMC
• Weighing Milky Way and Andromeda in an expanding $\Lambda$CDM Universe: Decreasing the Local Group mass
• Constrained cosmological simulations of the Local Group using Bayesian hierarchical field-level inference
• Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External Galaxies with the Nancy Grace Roman Space Telescope
• Following the tidal trail: a history of modeling the Magellanic Stream
• A Simulation Based Inference Approach to the Dynamics of the MW-LMC System -- Validation
• The outskirts of M33: Tidally induced distortions versus signatures of gas accretion
• Line-of-Sight Velocity Projection Impact on the Local Group Mass
• Machine Learning the Dark Matter Halo Mass of Milky Way-Like Systems
• Timing Mass of the Local Group
• The Milky Way and M31 Orbital History: Did the Local Group evolve in isolation?
• Impact of merger histories on the timing argument estimate of the Local Group mass