Annu. Rev. Astron. Astrophys. 1978. 16: 103-39
Copyright © 1978 by . All rights reserved

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4.2. Large-Scale Effects of Nuclear Activity

The unusual large-scale morphological and kinematical features that are found in the radio and optical observations of a few galaxies have been interpreted by some authors as the consequence of the expulsion of gas at high speeds from the nuclei. Two classic examples are M82 and NGC 1275 (Burbidge et al. 1963). However, the increasing complexity of the observational data obtained in the last few years has led to an increasing diversity of explanations: The peculiar appearance of M82 has been ascribed to an encounter of the galaxy with a cloud of gas, possibly swept up during a recent close interaction with M81 (Gottesman & Weliachew 1977; see also Cottrell 1977). Solinger et al. (1977) consider it possible that M82 has recently captured a cloud of intergalactic dust. In the case of NGC 1275, Rubin et al. (1977) have suggested that the high-velocity gas may be interpreted as constituting an intervening late-type galaxy.

Perhaps the best case for large-scale effects of nuclear explosions is to be made with NGC 4258. The broad, extensive, anomalous radio continuum and Halpha arms have been analyzed in some detail as arising from the interaction of gas expelled from the nucleus with gas further out in the disk (van der Kruit et al. 1972). Later observations of the kinematics of the gas provide at least a qualitative agreement with the predictions of the model (van der Kruit 1974b, van Albada & Shane 1975), although the rather modest disturbance of the HI distribution and kinematics is somewhat disappointing considering the spectacular nature of the radio continuum picture. Further discussion of this galaxy can be found in the papers by Oort (1974, 1975).

Evidence for large-scale disturbances of galaxies by nuclear activity has also been found in NGC 1569 (Hodge 1974b) and in NGC 5253 (Sersic et al. 1972). In particular for NGC 1569, de Vaucouleurs et al. (1974) have observed a complex velocity field which they suggest may be the result of ejection of matter from the nucleus in two opposing directions.

A number of galaxies selected on the basis of their radio continuum morphology have been offered as examples in this class by de Bruyn (1977b), who also estimated the lifetimes of the observable features as 107 to 5 × 108 years. The fact that about 10% of the luminous massive spirals show evidence for this sort of activity could then be interpreted to mean that every large disk galaxy experiences recurrences of these phenomena every 108 to 5 × 109 years.

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