INFRARED AND OPTICAL MORPHOLOGIES OF DISTANT RADIO GALAXIES

Multicolor line and continuum images of a complete sample of 13 3C radio galaxies at 0.8 < z < 1.3, spanning the range 2500 angstrom to 1-mu-m in the rest frame, are presented and analyzed. Quantitative analysis of these images shows that the infrared images are less elongated than those at optical wavelengths and show only a much weaker "alignment effect" with the radio source axis. The quadrupole moments show a progressive reduction from short to long wavelengths, as expected if a symmetric component dominates at infrared wave-lengths. A spectral decomposition based on these moments suggests that the aligned component probably has a roughly flat spectral energy distribution in f-nu, while the symmetric red component that dominates in the infrared probably has a spectral energy distribution similar to that of a gE galaxy. In typical 3C galaxies at z = 1, the active aligned component contributes 10% of the infrared light. While more active objects have a larger contamination, these generally modest components are insufficient to perturb significantly either the scatter in, or the continuity of, the observed K-z relation. The conventional interpretation of the K-z diagram in terms of a uniform population of mature host galaxies is thus still likely to be correct. As far as can be determined from the data, the scale sizes of the radio galaxy images at infrared wavelengths are consistent with the sizes of the giant ellipticals associated with powerful radio galaxies at low redshift. Several of these radio galaxies are accompanied by small red companion galaxies that are prominent on our infrared images at random position angles relative to the radio axis. These are interpreted as representing a conventional trigger for the radio sources. There is a preference for these companions to be associated with the bluest, most aligned, and generally most active objects.