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Published online by Cambridge University Press: 12 April 2016
The excitation mechanism of the extended emission-line regions (EELRs) in Seyfert galaxies is commonly thought to be nuclear photoionization. However, some Seyfert galaxies have EELRs with disturbed kinematics, outflows, and morphology which is indicative of interaction between radio plasma and the ISM of the host galaxy. In these cases shock excitation must also be considered (BickneU 1993).
To investigate the importance of shocks and photoionization, we have taken two approaches: mapping the spatial dependence of the line ratios, and using UV line ratios which are sensitive discriminants between shocks and photoionization.