Abstract
We report the results obtained from a study, based on long-slit spectroscopy, of the kinematics and ionization mechanisms of the line-emitting gas for a sample of five high/intermediate-redshift radio galaxies. In two of the galaxies (3C352 and 3C435A) the radio sources are of the same scale as the emission-line regions, whereas in the other three (3C34, 3C265 and 3C330) the radio sources are extended on a larger scale than the emission-line structures. We see evidence for shock-acceleration of the emission-line gas in the extended regions of all the galaxies, even in the largest radio sources of our sample, in which the radio hot spots have passed the extended gas of the galaxies. The extended regions present highly disturbed kinematics (line-splitting and/or underlying broad components), which are difficult to explain if we do not consider a strong interaction between the radio-emitting components and the ambient gas. However, the dominant ionization mechanism of the line-emitting gas remains uncertain. We have compared the optical diagnostic line ratios of the galaxies in our sample with both photoionization from the active galactic nucleus (AGN) and shock-ionization models. We find a lack of consistency in explaining the main ionization mechanism. This suggests that, if the extended regions are shock-ionized, some of the asumptions implicit in the models may need to be reconsidered.
