Optical identifications of faint ultra-steep spectrum radio sources

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, are presented. The sample, with a spectral index >1.1, is ∼25 times fainter than the 4C-sample of USS sources. Here, high-resolution follow-up observations with the VLA, deep optical imaging and some spectroscopy are described.