SPECTROPHOTOMETRY OF A SAMPLE OF 7C GIANT RADIO-SOURCES

We present spectrophotometric measurements of a sample of 7C classical double radio sources selected to have angular sizes 1.5 less than or equal to theta less than or equal to 3 arcmin and flux densities 0.4 l ess than or equal to S(151 MHz)less than or equal to 1.0 Jy. We find t hat these sources lie at redshifts out to at least 1 and have projecte d linear sizes approximate to Mpc. These objects provide the first evi dence that giant radio sources do not become less common at high redsh ift, and rule out the possibility that large radio sources are confine d by a medium which rapidly increases in density at high redshift. The sample provides additional support for unified schemes of powerful ra dio galaxies and radio quasars.