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Published online by Cambridge University Press: 12 April 2016
Photoionization and shock models of the extended emissionline regions (EELRs) in active galaxies demonstrate that the optical emission lines alone are a poor discriminant of the excitation mechanism. Combining optical and UV data provides a discriminant between nuclear photoionization and autoionizing shock models. Hubble Space Telescope UV spectrophotometry of two Seyferts suggests that the EELRs in these objects are probably photoionized by the nucleus.