Three‐dimensional Simulations of the Parker Instability in a Uniformly Rotating Disk

We investigate the effects of rotation on the evolution of the Parkerinstability in an exponentially-stratified and uniformly-rotating magnetizedgas disk by carrying out three-dimensional numerical simulations with anisothermal magnetohydrodynamic code. The instability has been initialized byrandom velocity perturbations. In the linear stage, the evolution is not muchdifferent from that without rotation and the mixed (undular + interchange) moderegulates the system. The interchange mode induces alternating dense andrarefied regions with small radial wavelengths, while the undular mode bendsthe magnetic field lines in the plane of azimuthal and vertical directions. Inthe nonlinear stage, flow motion overall becomes chaotic as in the case withoutrotation. However, as the gas in higher positions slides down along field linesforming supersonic flows, the Coriolis force becomes important. As oppositelydirected flows fall into valleys along both sides of magnetic field lines, theyexperience the Coriolis force toward opposite directions, which twists magneticfield lines there. Hence, we suggest that the Coriolis force plays a role inrandomizing magnetic field. The three-dimensional density structure formed bythe instability is still sheet-like with the short dimension along the radialdirection, as in the case without rotation. However, the long dimension is nowslightly tilted with respect to the mean field direction. The shape of highdensity regions is a bit rounder. The maximum enhancement factor of thevertical column density relative to its initial value is about 1.5, which issmaller than that in the case without rotation. We conclude that uniformrotation doesn't change our point of view that the Parker instability alone isnot a viable mechanism for the formation of giant molecular clouds.Comment: Accepted for publication in ApJ, 26 text pages with 9 figure