paper

The Stability of Disks in Cusped Potentials

arXiv:astro-ph/0006198 · doi:10.1086/318228

Abstract

We confirm that a high rate of shear at the center is able to stabilize an entire stellar disk against bar-forming (m=2) modes, irrespective of the dark halo density. Our simulations of unstable power-law disks also yield the growth rate and pattern speed of the dominant lop-sided (m=1) mode in close agreement with that predicted by linear theory in our cleanest case. The one-armed modes, which dominate models with extensive disks, can be controlled by tapering the outer disk. Two-armed instabilities of hard-centered disks are more difficult to identify because they are easily overwhelmed by particle noise. Nevertheless, we have detected the predicted m=2 modes in simulations with very large numbers of particles. Such bisymmetric instabilities in these disks are provoked only by sharp edges and are therefore easily eliminated. We have constructed a cool disk model with an almost flat rotation curve and a quasi-exponential density profile that is unambiguously stable. The halo in this stable model has a large core radius, with the disk and bulge providing almost all the rotational support in the inner parts.

27 pages LaTeX with 8 figures, revised version to appear in ApJ (full resolution figs 4 & 8 at http://www.physics.rutgers.edu/~sellwood/cuspy_disks.ps.tar.gz

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