An Iterative Method for the Construction of Equilibrium N-Body Models for Stellar Disks

Abstract

One widely used technique for the construction of equilibrium models of stellar disks is based on the Jeans equations and the moments of velocity distribution functions derived using these equations. Stellar disks constructed using this technique are shown to be "not entirely" in equilibrium. Our attempt to abandon the epicyclic approximation and the approximation of infinite isothermal layers, which are commonly adopted in this technique, failed to improve the situation substantially. We conclude that the main drawback of techniques based on the Jeans equations is that the system of equations employed is not closed, and therefore requires adopting an essentially ad hoc additional closure condition. A new iterative approach to constructing equilibrium N-body models with a given density distribution is proposed. The main idea behind this approach is that a model is first constructed using some approximation method, and is then allowed to adjust to an equilibrium state with the specified density and the required parameters of the velocity distribution remaining fixed in the process. This iterative approach was used to construct isotropic, spherically symmetric models and models of stellar disks embedded in an external potential. The numerical models constructed prove to be close to equilibrium. It is shown that the commonly adopted assumption that the profile of the radial velocity dispersion is exponential may be wrong. The technique proposed can be applied to a wide range of problems involving the construction of models of stellar systems with various geometries.

28 pages including 10 figures. To be published in Astronomy Reports (v. 50, No. 12, pp. 983-1000, 2006)

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• What Makes the Family of Barred Disc Galaxies So Rich: Damping Stellar Bars in Spinning Haloes
• Violent Buckling Benefits Galactic Bars
• Dark Matter Bars in Spinning Halos
• Stellar Bars in Counter-Rotating Dark Matter Halos: The Role of Halo Orbit Reversals
• The Coupling of Galactic Dark Matter Halos with Stellar Bars
• Bending instability in galactic discs. Advocacy of the linear theory
• The Origin of Buckling Instability in Galactic Bars: Searching for the Scapegoat
• Stellar Bars in Spinning Halos: Delayed Buckling and Absence of Slowdown
• GalMod: a Galactic synthesis population model
• Reconstructing the velocity dispersion profiles from the line-of-sight kinematic data in disc galaxies
• Phase models of the Milky Way stellar disc
• Bar-driven Leading Spiral Arms in a Counter-rotating Dark Matter Halo
• Made-To-Measure Models of Self-Similar Triaxial Halos with Steep Inner Density Gradients