The tangential velocity excess of the Milky Way satellites

Abstract

We estimate the systemic orbital kinematics of the Milky Way classical satellites and compare them with predictions from the Λ cold dark matter (ΛCDM) model derived from a semi-analytical galaxy formation model applied to high resolution cosmological N-body simulations. We find that the Galactic satellite system is atypical of ΛCDM systems. The subset of 10 Galactic satellites with proper motion measurements has a velocity anisotropy, β=-2.2$\pm$0.4, that lies in the 2.9% tail of the ΛCDM distribution. Individually, the Milky Way satellites have radial velocities that are lower than expected for their proper motions, with 9 out of the 10 having at most 20% of their orbital kinetic energy invested in radial motion. Such extreme values are expected in only 1.5% of ΛCDM satellites systems. This tangential motion excess is unrelated to the existence of a Galactic "disc of satellites". We present theoretical predictions for larger satellite samples that may become available as more proper motion measurements are obtained.

arXiv comment5 pages, 5 figures, MNRAS Letters accepted version; v2 - extended discussion on proper motion uncertainties

References in corpus (32)

• Dark Matter Substructure in Galactic Halos
• Where are the missing galactic satellites?
• The observed properties of dwarf galaxies in and around the Local Group
• Too big to fail? The puzzling darkness of massive Milky Way subhaloes
• Resolving Cosmic Structure Formation with the Millennium-II Simulation
• Galaxy formation in the Planck Cosmology - I. Matching the observed evolution of star formation rates, colours and stellar masses
• The APOSTLE simulations: solutions to the Local Group's cosmic puzzles
• A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy
• Third-Epoch Magellanic Cloud Proper Motions I: HST/WFC3 data and Orbit Implications
• Dark matter and cosmic structure
• The Present and Future Mass of the Milky Way Halo
• The great disk of Milky-Way satellites and cosmological sub-structures
• The Role of Dwarf Galaxy Interactions in Shaping the Magellanic System and Implications for Magellanic Irregulars
• The Masses of the Milky Way and Andromeda galaxies
• The Distribution of Satellite Galaxies: The Great Pancake
• The rotationally stabilized VPOS and predicted proper motions of the Milky Way satellite galaxies
• Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies
• The Space Motion of Leo I: Hubble Space Telescope Proper Motion and Implied Orbit
• Estimating the dark matter halo mass of our Milky Way using dynamical tracers
• Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. IV: Measurement for Sculptor
• Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. V: Final Measurement for Fornax
• The Copernicus Complexio: a high-resolution view of the small-scale Universe
• Planes of satellite galaxies: when exceptions are the rule
• Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. III: Measurement for Ursa Minor
• Determining orbits for the Milky Way's dwarfs
• The Spatial Distribution of Galactic Satellites in the LCDM Cosmology
• The Orbital Ellipticity of Satellite Galaxies and the Mass of the Milky Way
• A new spin on disks of satellite galaxies
• Proper Motion of the Leo II Dwarf Galaxy Based On Hubble Space Telescope Imaging
• Proper Motion of the Draco Dwarf Galaxy Based On Hubble Space Telescope Imaging
• Proper Motion of the Draco Dwarf Galaxy from Subaru Suprime-Cam Data
• A Hubble Astrometry Initiative: Laying the Foundation for the Next-Generation Proper-Motion Survey of the Local Group

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• The Milky Way's Disk of Classical Satellite Galaxies in Light of Gaia DR2
• The M101 group complex: new dwarf galaxy candidates and spatial structure
• Abundance matching with the mean star formation rate: there is no missing satellites problem in the Milky Way above ${\mathbf{M}}_{200}\sim 10^9{\mathbf{M}}_{\odot }$
• Planes of satellites around Milky Way/M31-mass galaxies in the FIRE simulations and comparisons with the Local Group
• The multiplicity and anisotropy of galactic satellite accretion
• Constraining the Milky Way Mass Profile with Phase-Space Distribution of Satellite Galaxies
• Evolution of galactic planes of satellites in the EAGLE simulation
• The velocity anisotropy of the Milky Way satellite system
• 3D hydrodynamic simulations for the formation of the Local Group satellite planes
• Inhomogeneous cosmology and backreaction: Current status and future prospects
• ZOMG III: The effect of Halo Assembly on the Satellite Population
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• Gaia EDR3 proper motions of Milky Way dwarfs. II: Velocities, Total Energy and Angular Momentum
• On the Effect of the Large Magellanic Cloud on the Orbital Poles of Milky Way Satellite Galaxies
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• We are not the 99 percent: quantifying asphericity in the distribution of Local Group satellites
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• A Study of the Properties and Dynamics of the Disk of Satellites in a Milky-Way-like Galaxy System
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