Discovery of an Obscured Broad-Line Region in the High-Redshift Radio Galaxy MRC 2025-218.

This Letter presents infrared spectra taken with the newly commissioned near-infrared spectrometer (NIRSPEC) on the Keck II telescope of the high-redshift radio galaxy MRC 2025-218 (z = 2.63). These observations represent the deepest infrared spectra of a radio galaxy to date and have allowed for the detection of Hβ, [O III] λλ4959, 5007, [O I] λ6300, Hα, [N II] λλ6548, 6583, and [S II] λλ6716, 6713. The Hα emission is very broad (FWHM = 9300 km s-1) and luminous (2.6 × 1044 ergs s-1), and it is very comparable to the line widths and strengths of radio-loud quasars at the same redshift. This strongly supports active galactic nucleus unification models linking radio galaxies and quasars, although we discuss some of the outstanding differences. The line [O III] λ5007 is extremely strong and has extended emission with large relative velocities toward the nucleus. We also derive that if the extended emission is due to star formation, each knot has a star formation rate comparable to a Lyman-break galaxy at the same redshift.