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Session 39 - AGNs, QSOs, Active Galaxies.
Display session, Wednesday, June 11
South Main Hall,
We discuss the role of shocks in powerful radio galaxies, with particular reference to a detailed optical spectroscopic study of a sample of sources at z < 0.5. In this sample we find convincing evidence that the spatial distribution, kinematics and physical conditions of the extended emission line regions (EELR) are defined by shocks induced by interaction between the radio jets and the warm interstellar medium. In view of the apparent importance of shocks in these sources, the possibility of shock ionization must be considered. We find that the emission line ratios in the shocked EELR are systematically different from those measured in the inner nuclear regions of the same sources, and ao from the line ratios measured in the EELR of other nearby radio galaxies which do not show the kinematical or morphological signs of shocks. A comparison of the observed line ratios with the predictions of shock models and photoionization models provides further evidence that shock ionization may be important. The similarities between the our sample of radio galaxies and those at higher redshifts (z \ge 1) suggest a major role for shocks in high redshift radio galaxies.
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