Probing non-spherical dark halos in the galactic dwarf galaxies

Kohei Hayashi, Masashi Chiba

Research output: Contribution to journalArticlepeer-review

56 Citations (Scopus)


We construct axisymmetric mass models for dwarf spheroidal (dSph) galaxies in the Milky Way to obtain plausible limits on the non-spherical structure of their dark halos. This is motivated by the fact that the observed luminous parts of the dSphs are actually non-spherical and cold dark matter models predict non-spherical virialized dark halos. Our models consider velocity anisotropy of stars v2R/ v2φ, which can vary with the adopted cylindrical coordinates under the assumption v2 Z= v2Rfor simplicity, and also include an inclination of the system as a fitting parameter to explain the observed line-of-sight velocity dispersion profile. Applying these models to six of the bright dSphs in the Milky Way, we find that the best-fitting cases for most of the dSphs yield oblate and flattened dark halos, irrespective of assumed density profiles in their central parts. We also find that the total mass of the dSphs enclosed within a spheroid with major-axis length of 300pc varies from10 6 M to107 M , contrary to the conclusion from spherical models. This suggests the importance of considering shapes of dark halos in mass models of the dSphs. It is also found that dark halos of the Galactic dSphs may be more flattened than N-body predictions, thereby implying our yet incomplete understanding of baryonic and/or non-baryonic dark matter physics in dwarf galaxy scales.

Original languageEnglish
Article number145
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 2012 Aug 20
Externally publishedYes


  • Local Group
  • dark matter
  • galaxies: dwarf
  • galaxies: kinematics and dynamics
  • galaxies: structure

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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