Published online by Cambridge University Press: 14 August 2015
As a theoretical subject, the study of the bending of the gaseous planes of galaxies has not been extremely popular. It seems that this is due to an excellent and thorough paper on the subject, published by Hunter and Toomre in 1969. At that time there existed three (or four) rival theoretical mechanisms:
(1) vertical oscillations of the galactic disk, considered first by Lynden-Bell (1965);
(2) asymmetrical pressure on the disk due to intergalactic wind (Kahn and Woltjer 1959);
(3) tidal influence of the Magellanic Clouds, from
(a) the case of Stationary Clouds, and
(b) the case of Clouds orbiting around the Galaxy (Elwert and Hablick 1965, Avner and King 1967).