The near-infrared camera on the W. M. Keck telescope has been used to image the z = 3.8 radio galaxy 4C 41.17. The 2 micron continuum consists of a thin arc of emission aligned along the radio axis. There is close correlation between the optical, infrared, and radio emission. The color of 4C 41.17 is blue (R - K_S_ = 2.7 +/- 0.1 mag). This may indicate ongoing star formation, but the origin of the continuum emission remains unclear. [O III] and Hβ emission makes a large contribution to the X-band flux. A number of faint red companions of 4C 41.17 are detected in the 2 micron image. If these sources are at the same redshift as 4C 41.17, then their red colors indicate ages of more than ~0.5 Gyr and an epoch of formation at z >~ 8.
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Graham et al. (1994) studied this question.