KECK OBSERVATIONS OF THE MOST DISTANT GALAXY - 8C-1435+63 AT Z=4.25

We report on Keck observations and confirm the redshift of the most di stant galaxy known: 8C 1435 + 63 at z = 4.25. The spectrum shows a str ong Lyalpha line, a Lyalpha forest continuum break and a continuum bre ak at lambda(rest) = 912 angstrom. The Lyalpha emission is spatially e xtended and roughly aligned with the radio source. The galaxy shows a double structure in the I-band (lambda(rest) almost-equal-to 1500 angs trom) which is aligned with the radio axis; the two I-band components spatially coincide with the nuclear and southern radio components. Som e fraction of the I-band emission could be due to a nonthermal process such as inverse Compton scattering. In the K-band (lambda(rest) almos t-equal-to 4200 angstrom), which may be dominated by starlight, the ga laxy has a very low surface brightness, diffuse morphology. The K morp hology shows little relationship to the radio source structure, althou gh the major axis of the K emission is elongated roughly in the direct ion of the radio source axis. The galaxian continuum is very red (I - K > 4) and if the K continuum is due to starlight, implies a formation redshift of z(f) > 5. We speculate that this galaxy may be the progen itor of a present-day cD galaxy.