A model of tidal interactions within the NGC 4631 group of galaxies.

A model of tidal interactions between the galaxies NGC 4631, 4656 and 4627 is proposed. The 21 cm observations of Weliachew et al. (1977) display four features of neutral hydrogen around NGC 4631; two of them can be explained in terms of a parabolic encounter between the two main galaxies NGC 4631 and 4656. The other two features may be interpreted with the help of the neighbouring galaxy NGC 4627: its mass is too small to perturb significantly the two other galaxies, but it undergoes itself a large damage; though NGC 4627 is classified now as a dwarf elliptical galaxy, it is assumed to have been an irregular or spiral galaxy in the past and to have lost its neutral gas in the recent encounter. This assumption is supported by the presence of rather young stars in this small galaxy.