A COMPLETE SAMPLE OF SOURCES IN THE NORTH ECLIPTIC CAP, SELECTED AT 38 MHZ .2. CCD OBSERVATIONS AND THEIR IMPLICATIONS

We present 55 CCD images and six spectra of a complete sample of 57 8C radio sources selected at 38 MHz in the North Ecliptic Cap. All but eight sources appear to be optically identified to a limiting magnitude of R almost-equal-to 23.5. Using spectroscopic redshifts where available and redshift estimates from the R magnitudes of the identifications otherwise, together with data on a bright comparison sample, we investigate the dependence of radio spectral index and physical size on redshift and radio luminosity. We find evidence that spectral index is more strongly correlated with redshift than with radio luminosity, and that there is a weak anticorrelation of size with redshift. The number density evolution seen within and between the samples is discussed, as are the relative fractions of quasars and cluster halo sources in the two samples. We also comment on the use of radio spectral indices in the search for distant radio galaxies.