5.8 Interacting Galaxies

Galaxies that show the effects of mutual interaction need not be extensively discussed here. They clearly represent tidal perturbations (Toomre and Toomre 1972), and the classification system need not be changed to accommodate them. But the forms are so interesting in themselves that a few illustrations (Plate 8) are useful.

Plate 8. Various interacting galaxies showing the effects of tidal distortion. This is not a representative sample such as the compilations of Vorontsov-Velyaminov (1959) or of Arp (1966).

An extensive compilation with photographs has been made by Vorontsov-Velyaminov (1959). Some such galaxies are illustrated in the series of photographs taken with large reflectors published in an atlas by Arp (1963). Studies of particular individual galaxies include papers by Zwicky (1956, 1959), Burbidge and Burbidge (1959), Sandage (1963), Sersic (1966), and others.

A general theory of interacting systems is discussed by Toomre and Toomre (1972), and for several particular systems by Limber (1965).