ar X iv : a st ro - p h / 99 09 16 1 v 1 9 S ep 1 99 9 HST imaging of two z > 4 radio galaxies

in both continuum and Lyα 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 Lyα 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. This object was observed in the F814W and F622W filters (F622W includes the Lyα line). Using the Lyα flux of Spinrad et al. 1995 we have produced a " pseudo-Lyα " image by scaling and subtracting the F814W image from the F622W one. In Fig. 1 we show the F814W image, the " pseudo-Lyα " image and the MERLIN 5GHz radio map superposed on the Keck K-band image of van Breugel et al. (1998). (The radio-optical registration should be accurate to ≈ 1 arcsec.) The Lyα peaks in the southern radio lobe, slightly offset from a faint patch of continuum emission. The central region has a (resolved) peak of UV emission surrounded by diffuse material. The K-band image shows that the rest-frame blue continuum is diffuse and covers the whole area enclosed by the radio lobes. The UV emission in the centre of the source is offset to the SW, but that in the southern lobe is closer to the major axis of the K-band emission. There is a suggestion of a bar of K-band emission perpendicular to the radio axis across the centre of the source. 6C 0140+326 One orbit in each of the F675W and F658N filters was obtained on this object. Both these filters contain the Lyα line, and the emission in the F675W filter was found to consist entirely of line emission. In addition, NICMOS imaging of a nearby high-z field galaxy has also given us a high signal:noise NIC3 image 1