[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 (z similar to 0.3) but less obscured in the even more radio-luminous galaxies seen at z similar to 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.