The behaviour of shape and velocity anisotropy in dark matter haloes

Abstract

Dark matter haloes from cosmological N-body simulations typically have triaxial shapes and anisotropic velocity distributions. Recently it has been shown that the velocity anisotropy, beta, of cosmological haloes and major merger remnants depends on direction in such a way that beta is largest along the major axis and smallest along the minor axis. In this work we use a wide range of non-cosmological N-body simulations to examine halo shapes and direction-dependence of velocity anisotropy profiles. For each of our simulated haloes we define 48 cones pointing in different directions, and from the particles inside each cone we compute velocity anisotropy profiles. We find that elongated haloes can have very distinct velocity anisotropies. We group the behaviour of haloes into three different categories, that range from spherically symmetric profiles to a much more complex behaviour, where significant differences are found for beta along the major and minor axes. We encourage future studies of velocity anisotropies in haloes from cosmological simulations to calculate beta-profiles in cones, since it reveals information, which is hidden from a spherically averaged profile. Finally, we show that spherically averaged profiles often obey a linear relation between beta and the logarithmic density slope in the inner parts of haloes, but this relation is not necessarily obeyed, when properties are calculated in cones.

23 pages, 14 figures. Accepted for publication in JCAP

References in corpus (10)

• A direct empirical proof of the existence of dark matter
• Strong and weak lensing united III: Measuring the mass distribution of the merging galaxy cluster 1E0657-56
• A universal density slope - velocity anisotropy relation for relaxed structures
• The Graininess of Dark Matter Haloes
• On Universal Halos and the Radial Orbit Instability
• An optimum time-stepping scheme for N-body simulations
• Dark Matter Halos: Velocity Anisotropy -- Density Slope Relation
• The haloes of merger remnants
• Spatial Anisotropy of Galaxy Kinematics in Sloan Digital Sky Survey Galaxy Clusters
• Asymmetric velocity anisotropies in remnants of collisionless mergers

Cited by in corpus (12)

• Halo-to-Halo Similarity and Scatter in the Velocity Distribution of Dark Matter
• Dissipative Dark Matter on FIRE: I. Structural and kinematic properties of dwarf galaxies
• SMBH Seeds from Dissipative Dark Matter
• Long range dark matter self-interactions and plasma instabilities
• Baryons Shaping Dark Matter Haloes
• Predicting the dark matter velocity distribution in galactic structures: tests against hydrodynamic cosmological simulations
• Globular Cluster Formation in the Virgo Cluster
• Perturbation theory with dispersion and higher cumulants: framework and linear theory
• EDGE: The shape of dark matter haloes in the faintest galaxies
• Particle ejection during mergers of dark matter halos
• A Gravitational Double Scattering Mechanism for Generating High Velocity Objects
• Dark matter scattering in astrophysical media: collective effects