A correlation between the radio and optical morphologies of distant 3Cr radio galaxies

The discovery of a strong correlation between the radio and optical morphologies of distant (z equal or greater than 0.6), powerful radio galaxies is reported. The isophotal axes of highly elongated distant 3CR galaxies, measured both in the light of stellar continua and extranuclear emission lines, tend to align with the radio source axes. This correlation suggests that there is a profound relation between these extremely powerful radio sources and their host galaxies. The most natural explanation of the effect is that the radio jets and/or backflows from the radio lobes interact with the interstellar media of the gas-rich galaxies associated with 3CR sources and stimulate large-scale star formation. This mechanism can provide a physical explanation for the high star formation and evolution rates of 3CR galaxies at large look-back times found in earlier photometric studies. Thus the formation and evolution of powerful radio galaxies and radio-quiet giant ellipticals may differ substantially.