A Detailed Study of the Complex Line-Emission Regions in the Radio Galaxy 3C34

We present the results of an extensive Fabry-Perot investigation of the extended line-emission gas surrounding powerful radio galaxies. High spatial (1.4 arcsec) and kinematical (400 km/s) resolution observations of the [OII]3727 emission-line of the powerful, double radio source 3C34 (z=0.689) are given. We present evidence that anisotropic radiation emanating from a hidden AGN is responsible for photoionizing a line-emission region extending more than 120 kpc. This is indicated by the distinctively bi-conical morphology of 3C34's [OII] gas. A number of line-emission components may also show various degrees of `shadowing' outward from the central ionizing source. A simple photoionization model is used to show that this interpretation is energetically viable on these length scales. The luminosity of the hidden central AGN, necessary to account for the observed [OII] luminosity, is compatible with that of a typical 3CR quasar at a similar redshift. Although this interpretation can account for the excitation and most of the unique shape of the warm gas, it is insufficient to explain the velocity and line-width structures observed with our Fabry-Perot interferometer. Therefore, we also propose that the illuminated medium surrounding 3C34 is the result of gas swept aside by the lateral expansion and backflow of the radio source lobes.