Nicmos Imaging of High-redshift Radio Galaxies

We have obtained near–infrared (1.6 µm) images of 11 powerful 3CR radio galaxies at redshifts 0.8 < z < 1.8 using NICMOS on board HST. The high angular resolution permits a detailed study of galaxy morphology in these systems at rest–frame optical wavelengths, where starlight dominates over the extended, aligned UV continuum. The NICMOS morphologies are mostly symmetric and are consistent with dynamically relaxed, elliptical host galaxies dominated by a red, mature stellar population. The aligned structures are sometimes faintly visible, and nuclear point sources may be present in a few cases which manifest the " unveiled " AGN that is obscured from view at optical wavelengths. Our observations are consistent with the hypothesis that the host galaxies of z ≈ 1 − 2 radio galaxies are similar to modern–day gE galaxies. Their sizes are typical of gE galaxies but smaller than present–day cD and brightest cluster galaxies, and their surface brightnesses are higher, as expected given simple luminosity evolution.