The peculiar radio galaxy B2 1637+29 : a high velocity encounter of two galaxy groups?

Radial velocity measurements are presented of several galaxies in the field of the peculiar radio galaxy B2 1637+29. We find that most galaxies are at the redshift of the radio galaxy, but a few also at that of the presumed companion of B2 1637+29. Since the difference in radial velocity between the two components is ∼ 4100 km s, the data seem to indicate that the two galaxies of the B2 1637+29 system are not physically connected, and that the double galaxy system is most probably the result of a chance superpostion of two unrelated groups or clusters of galaxies at different distances. On the other hand the unusual radio structure suggests interaction between the two galaxies, and this possibility is reinforced by a recent investigation of Colina & de Juan, who found signs of interaction based on the optical properties of the system. Some possible explanations of the system are given, but we conclude that for the moment the mystery of B2 1637+29 remains unsolved.