Results

In the 27 images studied, a total of 1030 radio peaks were detected above our 5 cutoff. A small fraction of these were deemed to be multiple, either because they were merged in the image or because two or more peaks were clearly associated with a particular galaxy. The final source count of 927 is approximate because of uncertainty over which sources are genuine doubles and which are unrelated point sources with a small projected separation. Table 2 shows the numbers and percentages of galaxies and stellar objects identified. The quoted (Poisson) errors indicate the significance of the observed fraction of identifications as a measure of the underlying average rate. Recall that we imposed a 2% chance probability limit. Given that about 26% of our sources have identifications we expect that at most (2/26) 100 = 7.7% are chance coincidences, i.e., the identification list is more than 92% reliable. The unidentified sources are expected to be associated with objects below the plate limit; results from Windhorst et al. (1984) suggest that the majority of these will be galaxies.

Our results can be compared with those of Unewisse (1993), who searched for optical identifications for 682 MOST radio sources in the fields of nearby rich clusters down to similar flux density limits, and found 173 (25%) non-stellar and 34 (5%) stellar identifications. We find the same fraction of possible QSO identifications and a slightly smaller fraction of galaxy identifications, but the difference is not significant.

© Copyright Astronomical Society of Australia 1997