OPTICAL IDENTIFICATIONS OF FAINT ULTRA-STEEP SPECTRUM RADIO-SOURCES

We present the first results of an observational study of ultra-steep spectrum sources selected on the basis of Westerbork surveys at 327 MHz complemented by observations at 608 MHz. The sample, with a spectral index > 1.1, is approximately 25 times fainter than the 4C-sample of USS sources first studied by Tielens et al. (1979) and currently by Chambers, Miley and van Breugel (1987). Here we describe high-resolution follow-up observations with the VLA, deep optical imaging (R(lim) approximately 23.7) and some spectroscopy. Elsewhere we discuss the implications of our observations. The decrease of the identification fraction with steepening spectral indexed observed in the 4C sample is also present in our faint source sample. We find no evidence for alignment between the optical and radio axes, and have not found any strong emission lines in a subsample for which we obtained low-resolution spectroscopy.