Shape and orientation of stellar velocity ellipsoids in spiral galaxies

Abstract

We present a numerical study of the properties of the stellar velocity distribution in stellar discs which have developed a saturated, two-armed spiral structure. We follow the growth of the spiral structure deeply into the non-linear regime by solving the Boltzmann moment equations up to second order. By adopting the thin-disc approximation, we restrict our study of the stellar velocity distribution to the plane of the stellar disc. We find that the outer (convex) edges of stellar spiral arms are characterized by peculiar properties of the stellar velocity ellipsoids, which make them distinct from most other galactic regions. In particular, the ratio σ_1:σ_2 of the smallest versus largest principal axes of the stellar velocity ellipsoid can become abnormally small (as compared to the rest of the disc) near the outer edges of spiral arms. Moreover, the epicycle approximation fails to reproduce the ratio of the tangential versus radial velocity dispersions in these regions. These peculiar properties of the stellar velocity distribution are caused by large-scale non-circular motions of stars, which in turn are triggered by the non-axisymmetric gravitational field of stellar spiral arms. The magnitude of the vertex deviation appears to correlate globally with the amplitude of the spiral stellar density perturbations. However, locally there is no simple correlation between the vertex deviation and the density perturbations. (Abstract abridged).

16 pages, 18 figures, Accepted for publication in MNRAS

References in corpus (3)

• New Constraints on the Galactic Bar
• The Effect of Spiral Structure on the Measurements of the Oort Constants
• Boltzmann moment equation approach for the numerical study of anisotropic stellar disks

Cited by in corpus (10)

• Using the PPML approach for constructing a low-dissipation, operator-splitting scheme for numerical simulations of hydrodynamic flows
• Simulations of Dynamical Gas-Dust Circumstellar Disks: Going Beyond the Epstein Regime
• Constraining Spiral Structure Parameters through Galactic Pencil-beam and Large-scale Radial Velocity Surveys
• Collisionless Stellar Hydrodynamics as an Efficient Alternative to N-body Methods
• The velocity ellipsoid in the Galactic disc using Gaia DR1
• The inner mass distribution of late-type spiral galaxies from SAURON stellar kinematic maps
• The vertex coordinates of the Galaxy's stellar systems according to the Gaia DR3 catalogue
• Spatial orientation and shape of the velocity ellipsoids of the Gaia DR3 giants and subgiants in the Galactic plane
• Stationary Spiral Structure and Collective Motion of the Stars in a Spiral Galaxy
• Peculiarities in the stellar velocity distribution of galaxies with a two-armed spiral structure