RADIO-CONTINUUM POLARIMETRIC IMAGING OF HIGH-REDSHIFT RADIO GALAXIES

Multifrequency images of total and polarized radio continuum emission from the two high redshift radio galaxies 0902+343 (z=3.40) and 0647+4 15 (4C 41.17, z=3.80) are presented. These images represent the most s ensitive polarimetric study of high redshift radio galaxies to date. T he emission from both galaxies is substantially polarized, up to 30% i n some regions, and both sources sit behind deep ''Faraday screens,'' producing large rotation measures, over 10(3) rad m(-2) in magnitude, and large rotation measure gradients across the sources. Such large ro tation measures provide further evidence that high redshift radio gala xies are situated in very dense environments. Drawing the analogy to a class of low redshift powerful radio galaxies with similarly large ro tation measures, we suggest that 0902+343 and 0647+415 are situated at the centers of dense, x-ray ''cooling flow'' clusters, and that the c luster gas is substantially magnetized. The remarkable similarity betw een the optical and radio morphologies of 0647+415 on scales as small as 0.1'' is presented. We consider, and reject, both synchrotron and i nverse Compton radiation as possible sources of the optical emission. We also consider both scattering of light out of a ''cone'' of radiati on from an obscured nucleus, and jet-induced star formation, and find that both models encounter difficulties in explaining this remarkably close radio-optical alignment. High resolution spectral index images r eveal compact, flat spectrum components in both sources. We suggest th at these components are the active nuclei of the galaxies. Lastly, hig h resolution images of 0902+343 show that the southernmost component f orms a ''ring'' of 0.2'' radius. We discuss the possibility that this ring is the result of gravitational lensing, along the lines proposed by Kochanek and Lawrence [AJ, 99, 1700 (1990)].