Is the dark halo of our Galaxy spherical?

Abstract

It has been recently claimed that the confined structure of the debris from the Sagittarius dwarf implies that the dark-matter halo of our Galaxy should be nearly spherical, in strong contrast with predictions from cold dark-matter (CDM) simulations, where dark halos are found to have typical density axis ratios of 0.6 - 0.8. In this letter, numerical simulations are used to show that the Sagittarius streams discovered thus far are too young dynamically to be sensitive to the shape of the dark halo of the Milky Way. The data presently available are entirely consistent with a Galactic dark-matter halo that could either be oblate or prolate, with minor-to-major density axis ratios c/a as low as 0.6 within the region probed by the orbit of the Sagittarius dwarf.

6 pages, 5 figures, MNRAS in press. Various changes to the discussion section, typos fixed, 2 new figures and more references added, conclusions unchanged. High-resolution figures available from http://www.astro.rug.nl/~ahelmi/research/flattening.html

References in corpus (3)

• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• Sagittarius Tidal Debris 90 kpc from the Galactic Center
• Absolute Proper Motions to B~22.5: V. Detection of Sagittarius Dwarf Spheroidal Debris in the Direction of the Galactic Anticenter

Cited by in corpus (88)

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• The Effect of Gas Cooling on the Shapes of Dark Matter Halos
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• The Origin of the Bifurcation in the Sagittarius Stream
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: III. Constraints on the Flattening of the Galactic Halo
• The Influence of Sagittarius and the Large Magellanic Cloud on the Milky Way Galaxy
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• The Causes of Halo Shape Changes Induced by Cooling Baryons: Disks Versus Substructures
• The Alignment between the Distribution of Satellites and the Orientation of their Central Galaxy
• Internal Alignment of the Halos of Disk Galaxies in Cosmological Hydrodynamic Simulations
• The Shape of the Gravitational Potential in Cold Dark Matter Halos
• The Ital-FLAMES survey of the Sagittarius dwarf Spheroidal galaxy. I. Chemical abundances of bright RGB stars
• Dark matter response to galaxy formation
• A sharper view of Pal 5's tails: Discovery of stream perturbations with a novel non-parametric technique
• Probing the Shape of the Galactic Halo with Hyper-Velocity Stars
• Constraining the Milky Way Halo Potential with the GD-1 stellar stream
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• A Magellanic Origin for the Warp of the Galaxy
• The fine-grained phase-space structure of Cold Dark Matter halos
• Mapping the Galactic Halo VIII: Quantifying substructure
• Stellar Streams as Probes of Dark Halo Mass and Morphology: A Bayesian Reconstruction
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• Tidal evolution of disky dwarf galaxies in the Milky Way potential: the formation of dwarf spheroidals
• Whiting 1: the youngest globular cluster associated with the Sgr dSph
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• Is Ursa Major II the Progenitor of the Orphan Stream?
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• Kinematics of hypervelocity stars in the triaxial halo of the Milky Way
• Stray, swing and scatter: angular momentum evolution of orbits and streams in aspherical potentials
• The Geometry of Sagittarius Stream from Pan-STARRS1 3$\pi$ RR Lyrae
• The Structure of the Sagittarius Stellar Stream as Traced by Blue Horizontal Branch Stars
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• Fermi-LAT Observations of Gamma-Ray Emission Towards the Outer Halo of M31
• The ACS Survey of Galactic Globular Clusters XI: The Three-Dimensional Orientation of the Sagittarius Dwarf Spheroidal Galaxy and its Globular Clusters
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• Dark matter in galaxies
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• The Tidal Streams of Disrupting Subhaloes in Cosmological Dark Matter Haloes
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• The Importance of Interactions for Mass Loss from Satellite Galaxies in Cold Dark Matter Haloes
• A Tale Twice Told: The Luminosity Profiles of the Sagittarius Tails
• Dark Matter Interpretation of the Fermi-LAT Observations Toward the Outer Halo of M31
• Analysis of galactic tides and stars on CDM microhalos
• Sagittarius stream 3-d kinematics from SDSS Stripe 82
• An artificial neural network to discover Hypervelocity stars: Candidates in Gaia DR1/TGAS
• Modelling resonances and orbital chaos in disk galaxies. Application to a Milky Way spiral model
• Exploring the Sagittarius Stream with SEKBO Survey RR Lyrae Stars
• Dynamics of Gaseous Disks in a Non-axisymmetric Dark Halo
• Interaction between collisionless galactic discs and nonaxissymmetric dark matter haloes
• Quantifying tidal stream disruption in a simulated Milky Way
• Probing the Halo From the Solar Vicinity to the Outer Galaxy: Connecting Stars in Local Velocity Structures to Large-Scale Clouds
• Detecting the Figure Rotation of Dark Matter Halos with Tidal Streams
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• The Next Generation Virgo Cluster Survey. XIX. Tomography of Milky Way Substructures in the NGVS Footprint
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• Revisiting the luminosity function of single halo white dwarfs
• The Milky Way Galaxy as a Strong Gravitational Lens
• MACHOs in dark matter haloes
• Applying Noether's theorem to matter in the Milky Way: evidence for external perturbations and non-steady-state effects from Gaia Data Release 2
• The interaction of dark matter cusp with the baryon component in disk galaxies
• Jeans that fit: weighing the mass of the Milky Way analogues in the $\Lambda \mathrm{CDM}$ universe
• Halo Geometry and Dark Matter Annihilation Signal
• Observational Constraints on the Modified Gravity Model (MOG) Proposed by Moffat: Using the Magellanic System
• Searching Extra-tidal Features around the Globular Cluster Whiting 1
• Miyamoto-Nagai discs embedded in the Binney logarithmic potential: analytical solution of the two-integrals Jeans equations
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• Variable gravitational potential of Milky Way analogues in HESTIA suite
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• Investigating the origin of the Milky Way streams. A revised look at their orbital pole distribution in light of precession effects
• Formation of dwarf galaxies and small-scale problems of CDM