[O III] 500.7 spectroscopy of 3C galaxies and quasars at redshift z > 1

We present near infrared spectra of z > 1 quasars and radio galaxies from the 3CR and 3CRR catalogues. [O iii] is detected in all but six of the 28 objects. These data extend the known correlation between the [O iii] and radio luminosities of radio sources to higher radio luminosities with no increase in scatter. The previously reported difference in [O iii] luminosities between radio-luminous galaxies and quasars at z < 0.8 is smaller at higher redshift and/or radio luminosity. In the context of orientation-based unified schemes of radio galaxies and quasars, this implies that the [O iii] emitting region is partially hidden in the most radio-luminous galaxies seen at low redshift (zt less obscured in the even more radio-luminous galaxies seen at z∼1. Alternatively, such schemes do not apply to all objects — perhaps there is a class of radio galaxies with high excitation narrow emission lines but no luminous quasar nucleus. Equivalent widths of [O iii] in the z > 1 quasars are similar to those at lower z, implying no change in the excitation mechanism with z or radio luminosity.