DYNAMICS OF BINARY GALAXIES .2. CLOSE PAIRS

As part of a comprehensive study of binary galaxies, broadband optical CCD images and high resolution H I maps are presented for six close p airs of spiral galaxies. A previous paper [Chengalur, et al., ApJ, 419 , 30 (1993)] presented the results of a study of binary galaxies with wide separations. The current sample of close pairs was chosen from th e CfA redshift catalog using selection criteria that were objective an d completely independent of any previously known morphological peculia rities. Nonetheless, all the galaxies show some sign of interaction, i mplying that the selection criteria were sufficiently well tailored to choose physically associated pairs. All the galaxies show kinematical disturbances and have asymmetric rotation curves. Tidal tails and bri dges are clearly detected for some, and two pairs have a large common H I envelope. This common H I envelope also shows a large scale radial velocity gradient and gives the impression of being in rotation about a single kinematical axis. Tere is relatively good agreement between the optical and H I images, with similar tidal features being seen in both. The H I features, however, extend to a much larger galactocentri c radius than the corresponding optical features. In at least one case , however, the stellar disk appears relatively normal, while the H i d isk appears disturbed even towards the center of the galaxy. The syste matic velocity difference for the galaxy pairs has been measured quite accurately either from the integrated H I spectral profile, or from a global fit to the galaxy velocity fields. The median velocity differe nce for the six galaxy pairs is very small, approximately 20 km s-1. D etailed analysis of the data will be presented in a separate paper.