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Galaxies have been classified in six clusters which are known to emit X-rays. It is found that in all cases the ratio of the surface density of spiral galaxies to that of S0's increases outward. Moreover, there is a correlation between the velocity dispersion of the galaxies in a cluster and the overall proportion of S0's among disk galaxies. These facts are interpreted as support for Gunn and Gott's (1972) hypothesis that S0's are produced from spirals by a process in which the interstellar gas in spirals is swept out as these galaxies move through the hot gas presumed to be responsible for the X-ray emission. A further test of this hypothesis is suggested, and redshift measurements are presented for galaxies in several X-ray clusters.
Melnick et al. (Fri,) studied this question.