Radio galaxies at z=1.1 to 3.8:: Adaptive optics imaging and archival Hubble Space Telescope data

We have undertaken a program of high-resolution imaging of high-redshift radio galaxies (HzRGs), using adaptive optics on the Canada-France-Hawaii Telescope. We report on deep imaging in J, H, and K bands of six HzRGs in the redshift range 1.1 to 3.8. At these redshifts, near-infrared bandpasses sample the rest-frame visible galactic light. The radio galaxy is resolved in all the fields and is generally elongated along the axis of the radio lobes. These images are compared with archival Hubble Space Telescope Wide-Field Planetary Camera 2 optical observations of the same fields and show that the HzRG morphology in rest-frame ultraviolet and visible light is generally very similar: a string of bright compact knots. Furthermore, this sample-although very small-suggests that the colors of the knots are consistent with light from young stellar populations. If that is the case, a plausible explanation is that these objects are being assembled by mergers at high redshift.