Key points are not available for this paper at this time.
We have obtained Hubble Space Telescope (HST) WFC observations of CL 0939+4713, a very rich cluster at z = 0.41 which exhibits an excess population of blue galaxies typical of clusters at that redshift. The images are of sufficient quality, despite the HST spherical aberration problems, to permit assignment of Hubble types to galaxies brighter than r ~ 24.0. Their colors, luminosity functions and structure suggest that most of the galaxies are normal examples of their Hubble type. However, there is a significant number of objects which appear to be undergoing tidal interactions and/or mergers. These data suggest that the excess blue galaxies seen in distant clusters are predominantly normal late-type spirals but also that dynamical interactions between galaxies may be an important process in such clusters and may be responsible for those galaxies which exhibit spectroscopic signs of starbursts.
Dressler et al. (Fri,) studied this question.