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Title:
Stability of nonrotating stellar systems. II - Prolate shell-orbit models
Authors:
Merritt, David; Hernquist, Lars
Affiliation:
AA(Rutgers University, Piscataway, NJ), AB(Institute for Advanced Study, Princeton, NJ)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 376, Aug. 1, 1991, p. 439-457. Research supported by University of California and Pittsburgh Supercomputing Center. (ApJ Homepage)
Publication Date:
08/1991
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
Galactic Rotation, Galactic Structure, Shell Galaxies, Stellar Systems, Astronomical Models, Galactic Evolution, Many Body Problem, Systems Stability
DOI:
10.1086/170293
Bibliographic Code:
1991ApJ...376..439M

Abstract

The dynamical stability of nonrotating prolate galaxy models constructed from thin long-axis tube orbits ('shell' orbits) are investigated. Models more elongated than about E6 (axis ratio of about 2:5) are unstable to bending modes than rapidly increase the velocity dispersion perpendicular to the long axis and decrease the model's elongation. Approximate representations of the spatial forms of the fastest growing modes and their growth rates are obtained. Most of the evolution is due to two modes: a symmetric (banana-shaped) bending and an antisymmetric (S-shaped) bending. The instability is similar to the 'firehose' instability of a thin self-gravitating slab, except that it persists in models with velocity anisotropies that are much less extreme than the critical value for instability of the slab. A simple model is given that reproduces the basic features of the instability in the prolate geometry. These results provide support for the hypothesis of Fridman and Polyachenko (1984) that the absence of elliptical galaxies flatter than about E6 is due to dynamical instability.

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