The colours of faint radio galaxies - Finding ellipticals at Z greater than 0.5

It is noted that since the galaxy luminosity distribution is very wide and the color evolution as a function of cosmic epoch depends strongly on the time-dependent star formation rates, which probably means on galaxy type, it is not possible to relate, even approximately, the apparent magnitude and a single color of a faint galaxy image to its redshift. A method of forming substantially large samples of giant elliptical galaxies near the faint end of deep plate magnitude scales is described. The method involves a combination of deep radio images and optical plates of the same fields. It relies on the fact that strong extragalactic radio sources are, it not quasars, uniquely and without exception associated with luminous early-type galaxies, ellipticals, and S0's.