Stability of Disk Galaxies in the Modified Dynamics
Abstract
General analytic arguments lead us to expect that in the modified Newtonian dynamics (MOND), selfgravitating disks are more stable than their like in Newtonian dynamics. We study this question numerically, using a particlemesh code based on a multigrid solver for the (nonlinear) MOND field equation. We start with equilibrium distribution functions for MOND disk models having a smoothly truncated, exponential surface density profile and a constant Toomre Qparameter. We find that, indeed, disks of a given ``temperature'' are locally more stable in MOND than in Newtonian dynamics. As regards global instability to bar formation, we find that as the mean acceleration in the disk is lowered the stability of the disk is increased as we cross from the Newtonian to the MOND regime. The degree of stability levels off deep in the MOND regime, as expected from scaling laws in MOND. For the disk model we use, this maximum degree of stability is similar to the one imparted to a Newtonian disk by a halo 3 times as massive at 5 disk scale lengths.
 Publication:

The Astrophysical Journal
 Pub Date:
 July 1999
 DOI:
 10.1086/307402
 arXiv:
 arXiv:astroph/9811013
 Bibcode:
 1999ApJ...519..590B
 Keywords:

 GALAXIES: KINEMATICS AND DYNAMICS;
 INSTABILITIES;
 METHODS: NBODY SIMULATIONS;
 Galaxies: Kinematics and Dynamics;
 Instabilities;
 Methods: nBody Simulations;
 Astrophysics
 EPrint:
 20 pages, Latex, 8 embedded figures, version to be published in The Astrophys. J