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Galaxies do not exist in total isolation. They interact with their environment and they modify their surroundings through nuclear activity, galactic winds, tidal encounters and collisions. While this activity is not necessarily a continuous phenomenon, its effect on the dynamics and long-term evolution of galaxies and galactic systems is undoubtedly significant. Galaxies are the cumulative result of both quiescent and catastrophic evolution. It is the purpose of this Catalogue to highlight the most spectacular phases of galactic evolution, and perhaps formation, by drawing attention to the basic forms in which this activity is manifest.

In addition to cataloguing individual galaxies, the identification and study of associations is important. The relatively recent advent of wide-field, fast Schmidt telescopes has enabled the earlier emphasis on individual galaxies to be shifted to such associations. For example, at the turn of the century Keeler (1900, 1908), Curtis (1918), Pease (1917, 1920) and others published many remarkable large-scale prints of individual galaxies, as photographed by the small-field reflectors of the time. This individual approach to galaxies culminated in the production of atlases such as Evans' (1957) Cape Photographic Atlas of Southern Galaxies, Sersic's (1968) Atlas de Galaxies Australes, Sandage's (1961) Hubble Atlas of Galaxies and Sandage and Tammann's (1981) Revised Shapley-Ames Catalogue which were basically illustrative of classification systems based on symmetry, and focussed on single galaxies in isolation.

The Schmidt telescopes have therefore provided a new perspective, unavailable to earlier generations of extragalactic astronomers. Pairs, triples and clusters of galaxies became immediately apparent to the casual observer, whereas previously any associations had to be hunted laboriously out of catalogues and listings of uncertain completeness and/or reliability. The wide-field Schmidt also made it possible to survey the whole sky. A complete census of any given kind of object could be made and a statistical analysis could then be performed.

The Palomar Observatory Sky Survey, made with the 48-inch Schmidt, resulted in new galaxy and cluster searches being undertaken. For instance Abell (1958) catalogued and classified the relatively conspicuous clusters of galaxies, while Zwicky and his collaborators (Zwicky, Herzog and Wild 1960; Zwicky and Herzog 1963, 1966, 1968; Zwicky, Karpowicz and Kowal 1965; Zwicky and Kowal 1968) identified all galaxies down to mpg approx 15.5 mag, while also noting pairs, triples, etc. and outlining clusters.

Another of the outstanding contributions of the Schmidt telescope has been to locate among myriad galaxies just those that are spectacularly peculiar. The study of these objects has helped us understand some physical processes and at the same time confronts us with many more that we do not understand. Working from Sky Survey paper prints Vorontsov-Velyaminov (1959) produced an Atlas and Catalogue of Interacting Galaxies which was soon followed by Arp's (1966) Atlas of Peculiar Galaxies. While many of these objects were followed up and studied with large-aperture reflectors their relationship to neighbouring galaxies required the wide-field perspective afforded by the Schmidt telescopes.

Photography to slightly fainter surface-brightness levels than usual can often reveal the much larger outer areas of many galaxies. In turn these outer regions, being less dense, can reveal perturbations and distortions more easily. These perturbations can come from internal activity such as explosions or ejections, or from interaction with neighbouring objects. Naturally this means that the regions surrounding galaxies must be carefully studied. It is the combination of fainter surface-brightness detection and wide-field registration that enabled this new area of astronomical research to be opened up.

The introduction by Kodak of their fine-grained IIIa-J emulsion has made it practical to discover and study these faint features in a systematic way. So in combining the wide-field surveying capabilities of the Schmidt telescope and the deeply penetrating exposures of the IIIa-J emulsion, the SRC Southern Sky Survey has provided a unique source of data on peculiar galaxies and associations. We have used this source material to produce what we hope is a complete and detailed catalogue of all the most interesting galaxies and most striking apparent associations of galaxies in the southern sky.

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