An optically luminous radio galaxy at Z = 3.22 and the K-z diagram at high redshift

Images of the radio galaxy 6C 1232+39 taken through the B, R, I, J, H, and K filters, taken through a narrow-band filter centered on the Ly alpha line, and made with the VLA at 5 GHz are presented. This radio galaxy is found to have a 'classical double' radio structure, unlike the other two radio galaxies with z greater than 3 that have been extensively studied. It is shown that 6C 1232+39 has a red bump in its rest-frame optical spectrum, like the other two radio galaxies with z greater than 3. Evidence is presented which shows that the scatter in the K-z diagram at z greater than 2 is greater that the scatter at z less than 2. Lastly, it is suggested that the dispersion in the K-band magnitudes of the known radio galaxies with z greater than 2 raises doubts as to the use of the K-z Hubble relation to estimate the redshifts of distant radio galaxies from K magnitudes alone