Infrared studies of a sample of 3C radio galaxies

J, H and K photometry is presented for 35 3C radio galaxies spanning a large range of redshift. At low redshifts, z < 0.4, the near-infrared colours of most radio galaxies are the same as non-radio elliptical galaxies, except for the N-galaxies which show a strong infrared excess. At higher redshifts the galaxies show little evidence for spectral evolution in their infrared colours, but have optical-infrared colours considerably bluer than is predicted by a redshifted non-evolving energy distribution. The infrared Hubble diagram for the radio galaxies is constructed, and implies a high apparent value for q0, which may indicate evolution in the infrared luminosity of these galaxies. The results are discussed in the context of current models for the evolution of the stellar population of giant elliptical galaxies. (author)