The orientation of gas disks in tumbling prolate galaxies

Abstract

In Paper I, it has been suggested that dissipative processes coupled with the differential precession of particle orbits will cause gas flowing in a static spheroidal galaxy to settle into a preferred plane of the galaxy--namely, the equatorial plane of the spheroid. In this paper, we discuss the existence of preferred planes for gas which flows into a tumbling, prolate spheroidal (barlike) galaxy. We argue that this type of galaxy exhibits three different dynamical regions and that the preferred plane into which the gas will settle is not the same in all three regions. In particular, while gas in the outermost region of the galaxy aligns its orbital angular momentum vector with the spin axis of the tumbling bar, gas in the innermost region will align its angular momentum vector in a direction orthogonal to that axis, along the major axis of the bar. An analytic determination of the orientation of preferred planes in the case of a weak bar supports this picture. We suggest that NGC 2685 is an example of a galaxy in which orthogonally oriented disks have been observed. A dynamical classification scheme is outlined that encompasses all prolate elliptical galaxies and, perhaps, many barred spiral galaxiesmore » as well.« less