INFLUENCE OF A DARK HALO ON THE STABILITY OF ELLIPTIC GALAXIES

We describe N-body simulations to investigate whether the presence of dark matter in elliptical galaxies could inhibit the bar-making instability which is characteristic of systems with many stars on near-radial orbits. Our calculations show that neither a fixed static halo nor a halo composed of particles with isotropic velocity dispersions is very effective in suppressing the instability; thus the presence of a dark halo is not likely to affect conclusions about how anisotropic the velocities of stars in elliptical galaxies might be. Modifications of the Jeans-type stability criterion of Polyachenko and Shukman to include the effect of the halo are in agreement with our results for a halo of "live" particles but overestimate the stabilizing effect of a fixed halo potential. We also present evidence that the bar-making instability can change the radial density profile of our models, significantly reducing an initial high central concentration.