Preferred orbit planes in triaxial galaxies. II - Tumbling about a nonprincipal axis

A method from celestial mechanics is used to determine the preferred orbit planes into which gas will settle in the external potential of both spheroidal and triaxial galaxies tumbling about nonprincipal axes. These preferred planes are directly related to the locations of periodic orbits. The number and orientation of the preferred planes depend on the shape of the galaxy, the orbit radius, the tumble axis orientation, and the tumble rate. One of the major results of this work is that, for galaxies tumbling about a nonprincipal axis, the preferred planes exhibit warps and twists with increasing radial distance from the galaxy center. Because of this, steady state planar gas disks cannot exist in these galaxies. The present method permits determination of the precessional motions for gas orbits not in preferred planes. Diagrams are provided illustrating the geometry of this precessional motion. The implications of these results for warped and twisted gas disks both as observed in real galaxies and as expected for galaxies which form through a merger are briefly discussed.