Radial orbit instability in dwarf dark matter haloes

Abstract

Using N-body simulations we study the phenomenon of radial orbit instability occurring in dark matter haloes of the size of a dwarf galaxy. We carried out simulations of seven spherical models, with the same standard NFW density profile but different anisotropy profiles of particle orbits. Four of them underwent instability: two with a constant positive anisotropy, one with an anisotropic core and an isotropic envelope and one with a very small isotropic core and an anisotropic envelope. Haloes affected by the instability become approximately axisymmetric and prolate, with the profile of the shortest-to-longest axis ratio increasing with radius. The lower limit for the central value of this axis ratio is 0.3 for an NFW halo. The density profiles of the haloes did not change significantly, whereas the velocity distributions became axisymmetric. The total angular momentum rose due to large-amplitude oscillations of its components perpendicular to the symmetry axis of the halo. We also studied orbits of individual particles assigning them to classical orbit families in triaxial potentials. We find that the membership of a given particle in a family depends on its initial total angular momentum and its components along the principal axes of matter distribution.

14 pages, 10 figures, accepted by MNRAS

References in corpus (6)

• The distribution function of dark matter in massive haloes
• On Universal Halos and the Radial Orbit Instability
• The Role of the Radial Orbit Instability in Dark Matter Halo Formation and Structure
• Orbital anisotropy in cosmological haloes revisited
• The behaviour of shape and velocity anisotropy in dark matter haloes
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Cited by in corpus (9)

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• Recovering the mass profile and orbit anisotropy of mock dwarf galaxies with Schwarzschild modelling
• Tidally induced bars in gas-rich dwarf galaxies orbiting the Milky Way
• Discreteness effects, $N-$body chaos and the onset of radial-orbit instability
• Radially anisotropic systems with $r^{-\alpha }$ forces. II: radial-orbit instability
• Radially anisotropic systems with $r^{-\alpha }$ forces: equilibrium states