Westerbork Observations of 37 Poor Clusters of Galaxies at 1415 MHz

Summary

Observations of a sample of 37 poor clusters of galaxies north of declination +35° have been made at 1415 MHz with the Westerbork Synthesis Radio Telescope (WSRT). The poor cluster sample has been drawn from the Zwicky catalog by locating groups of three or more galaxies brighter than 15^m.7 where the surface density of galaxies exceeds the average surface density for all galaxies in the Zwicky catalog above 40° galactic latitude by at least a factor of 46.

In the 37 poor cluster fields observed, 204 radio sources with 1415 MHz flux densities greater than 10 mJy were detected. However, only 14 of these sources could be identified with galaxies that are poor cluster members. Half of the poor cluster radio sources are associated with galaxies that have close companions and, in some cases, that appear disrupted as a result of the encounter with the companion. The detection rate for galaxies with close companions was approximately five times greater than that for galaxies without close companions.

The morphologies of the identified poor cluster radio sources are not unusual — ten sources were unresolved and are probably confined to the nucleus of the associated galaxy, two are elongated at the same position angle as the associated galaxy and can be attributed to low-level disk emission, one is double, and one is a head-tail (the well known source B2 1615+35). Although several examples of head-tail radio galaxies in poor clusters are now known, the fact that further examples were not discovered in the current observations could indicate that the presence of an intracluster medium dense enough to distort the radio structure may be relatively uncommon in poor clusters of galaxies.