ar X iv : a st ro - p h / 99 04 27 2 v 1 2 1 A pr 1 99 9 A Radio Galaxy at z = 5 . 19 1

We report the discovery of the most distant known AGN, the radio galaxy TN J0924−2201 at z = 5.19. The radio source was selected from a new sample of ultra–steep spectrum (USS) sources, has an extreme radio spectral index α 365MHz = −1.63, and is identified at near–IR wavelengths with a very faint, K = 21.3± 0.3 object. Spectroscopic observations show a single emission line at λ ∼ 7530 Å which we identify as Lyα. The K–band image, sampling rest frame U–band, shows a multi–component, radio–aligned morphology, typical of lower–redshift radio galaxies. TN J0924−2201 extends the near–IR Hubble, or K − z, relation for powerful radio galaxies to z > 5, and is consistent with models of massive galaxies forming at even higher redshifts. Subject headings: cosmology: early universe – galaxies: active – galaxies: distances and redshifts – galaxies: formation – galaxies: individual: TN J0924−2201