Discovery of an obscured broad-line region in the high-redshift radio galaxy MRC 2025-218

Letter presents infrared spectra taken with the newly commissioned near-inf rared spectrometer (NIRSPEC) on the Keek II telescope of the high-redshift radio galaxy MRC 2025 - 218 (z = 2.63). These observations represent the de epest infrared spectra of a radio galaxy to date and have allowed for the d etection of H beta, [O III] lambda lambda 4959, 5007, [O I] lambda 6300, H alpha, [N II] lambda lambda 6548, 6583, and [S II] lambda lambda 6716, 6713 . The H alpha emission is very broad (FWHM = 9300 km s(-1)) and luminous (2 .6 x 10(44) ergs s(-1)), and it is very comparable to the line widths and s trengths of radio-loud quasars at the same redshift. This strongly supports active galactic nucleus unification models linking radio galaxies and quas ars, although we discuss some of the outstanding differences. The line [O I II] lambda 5007 is extremely strong and has extended emission with large re lative velocities toward the nucleus. We also derive that if the extended e mission is due to star formation, each knot has a star formation rate compa rable to a Lyman-break galaxy at the same redshift.