HST imaging of two z>4 radio galaxies

Abstract

We have imaged 8C 1435+635 (z=4.25; Lacy et al. 1994; Spinrad, Dey & Graham 1995) and 6C 0140+326 (z=4.41; Rawlings et al. 1996) in both continuum and Lyalpha plus continuum bands with the HST. Our images show patchy distributions of continuum and line emission with a tendency for the peaks in the two types of emission to be offset. When compared to Keck K-band images, it seems likely that the presence of dusty neutral gas is strongly influencing the UV continuum and Lyalpha emission. The radio and UV emission are not particularly well-correlated, except for a general tendency towards radio-optical alignment. It is suggested that at least some of the observed radio-optical alignment is produced as dust is cleared from the radio lobes by shocks associated by the radio source. If true, this means that 8C1435+635 could be hosting a luminous, galaxy-scale starburst, as suggested by submm observations.