Figure Rotation of Cosmological Dark Matter Halos

Abstract

We have analyzed galaxy and group-sized dark matter halos formed in a high resolution LCDM numerical N-body simulation in order to study the rotation of the triaxial figure, a property in principle independent of the angular momentum of the particles themselves. Such figure rotation may have observational consequences, such as triggering spiral structure in extended gas disks. The orientation of the major axis is compared at 5 late snapshots of the simulation. Halos with significant substructure or that appear otherwise disturbed are excluded from the sample. We detect smooth figure rotation in 278 of the 317 halos in the sample. The pattern speeds follow a log normal distribution centred at 0.148 h km/s/kpc with a width of 0.83. These speeds are an order of magnitude smaller than required to explain the spiral structure of galaxies such as NGC 2915. The axis about which the figure rotates aligns very well with the halo minor axis, and also reasonably well with its angular momentum vector. The pattern speed is correlated with the halo spin parameter, but shows no correlation with the halo mass. The halos with the highest pattern speeds show particularly strong alignment between their angular momentum vectors and their figure rotation axes. The figure rotation is coherent outside 0.12 r_vir. The measured pattern speed and degree of internal alignment of the figure rotation axis drops in the innermost region of the halo, which may be an artifact of the numerical force softening. The axis ratios show a weak tendency to become more spherical with time.

arXiv comment37 pages, 18 figures, submitted to ApJ

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• Ellipsoidal halo finders and implications for models of triaxial halo formation
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• The Tidal Streams of Disrupting Subhaloes in Cosmological Dark Matter Haloes
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• Loss of halo triaxiality due to bar formation
• On the relation between radial alignment of dark matter subhalos and host mass in cosmological simulations
• Influence of baryons on the orbital structure of dark matter haloes
• Internal Alignments of Red Versus Blue Discs in Dark Matter Halos
• Tidal Torquing of Elliptical Galaxies in Cluster Environments
• The Orbital Structure of Triaxial Galaxies with Figure Rotation
• An Analytic Model for the Axis-Ratio Distribution of Dark Matter Halos from the Primordial Gaussian Density Field
• Figure rotation of dark halos in CDM simulations
• Interaction between collisionless galactic discs and nonaxissymmetric dark matter haloes
• Detecting the Figure Rotation of Dark Matter Halos with Tidal Streams
• Dynamics of Stellar Disk Tilting from Satellite Mergers
• Charting Galactic Accelerations with Stellar Streams and Machine Learning
• Tilted outer and inner structures in edge-on galaxies?
• Drivers of disc tilting I: Correlations and possible drivers for Milky Way analogues
• The tilting rate of the Milky Way's disc
• Shape Profiles and Orientation Bias for Weak and Strong Lensing Cluster Halos
• Homeoidally striated density profiles. II. Anisotropy and rotation
• Elliptical galaxies: rotationally distorted, after all
• Variable gravitational potential of Milky Way analogues in HESTIA suite