On the Origin of the Ultraviolet Continuum Emission from the High-Redshift Radio Galaxy 3C 256

We report spectropolarimetric observations obtained with the W. M. Keck Telescope of the high-redshift (z = 1.824) aligned radio galaxy 3C 256. Our observations confirm that the spatially extended UV continuum emission from this galaxy is polarized (P_V_ ~ 10.9% +/- 0.9%) with the electric vector perpendicular to the aligned radio and optical major axes (θ_V_ ~ 48.0^deg^ + 2.4^deg^). This strongly suggests that a significant fraction of the rest frame UV continuum emission from the galaxy is not starlight, but is instead scattered light from a powerful active galactic nucleus that is hidden from our direct view. The narrow emission lines, including Mg II, are unpolarized. The percentage polarization of the continuum emission and the polarization position angle are roughly constant as a function of wavelength. Although the present data do not permit us to discriminate between cool electrons and dust as the origin of the scattering, scattering by a population of hot (T ~> 10^7^ K) electrons cannot be the dominant process, since such a population would overproduce X-ray emission. A large population of cooler electrons (T ~ 10^4^ K) could be responsible for both the line emission and the scattered light, but would require that the dust-to-gas ratio in the scattering cones is 10^-3^ times smaller than that in our Galaxy and would imply that a large fraction of the baryonic mass in the galaxy is in the ionized component of its interstellar medium. Dust scattering is more efficient, but would result in detectable extinction of the emission-line spectrum unless the dust distribution is more highly clumped than the line emitting gas. Finally, we detect a strong (W^rest^lambda_ ~ 12 A) broad (FWHM ~ 6500 km s^-1^) absorption line centered at λ_rest_ ~ 1477 A. We discuss several possibilities for its origin and conclude that the most likely candidate is absorption by a high-velocity broad absorption line cloud near the nucleus of 3C 256.