A new sample of giant radio galaxies from the WENSS survey - I. Sample definition, selection effects and first results

We have used the Westerbork Northern Sky Survey (WENSS) to define a sample of 47 low redshift (z less than or similar to 0.4) giant radio galaxies. This is the largest sample yet of such radio sources originating from a single survey. We present radio maps of the newly discovered giants and optical images and spectra of their host galaxies. We present some of their properties and discuss the selection effects. We investigate the distribution of the sources in the radio power - linear size P-D diagram, and how these parameters relate to the redshifts of the sources in our sample. We find a strong drop in the number of sources with a linear size above 2 Mpc. We argue that this is not a result of selection effects, but that it indicates either a strong luminosity evolution of radio sources of such a size, or that a large fraction of radio sources "switch off" before they are able to grow to a size of 2 Mpc.