Multiple Galaxies

Abstract

Investigators of extragalactic objects have occupied themselves successively with the study of individual galaxies, multiple galaxies, clusters of galaxies and, most recently, with intergalactic matter. While all of these studies, in the past, have gone their individual ways, it is now not only appropriate but necessary to consider the interrelations and the transitions between the various forms of the large scale aggregations of matter. These aggregations are in fact not at all as distinct units as are for instance the stars and atoms. The decision of whether or not a specific individual star, dust cloud or gas cloud belongs definitely to any given galaxy, group of galaxies or to an intergalactic formation is indeed at the present state of our knowledge an almost impossible one to make. In order to shed some light on this problem, we therefore propose in this article to outline directives for the future investigation of multiple galaxies. For this purpose we shall sketch some possible morphological and structural aspects of characteristic double and multiple galaxies. Referring to the history of the subject at hand, it should be mentioned that good photographs of double galaxies were probably first obtained by F. G. Pease with the 60-inch reflector of the Mount Wilson Observatory. Pease published his results in two classic papers [1] in 1917 and 1920.