Compact groups are intermediate between single and binary galaxy systems, and clusters of galaxies. Because of their small numbers of members, and the small separations between the members of each group, they are good candidates for the study of galaxy interactions and mergers. In particular, high resolution imaging of these systems in neutral hydrogen can yield important data on interactions between galaxies.
The radio telescopes of the Australian National Telescope Facility (ATNF) are especially well suited to the study of neutral hydrogen gas in these systems. The Parkes 64-m telescope has a 15 arcminute FWHM beam at 21 centimeters wavelength which is sufficient to include the sky area of a typical compact group. Parkes was used for detection of HI in nine southern groups and for determination of their approximate velocities, if not previously known. Follow-up observations with the ATNF Compact Array synthesis telescope provided high resolution (20 arcsecond) images with appropriate frequency resolution to determine velocity fields for the gas distribution.