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Line profiles for emission lines broadened by electron scattering are calculated and compared with Anderson's composite profile of the Balmer lines in the Seyfert galaxy NGC 5548. The computed profile for a model in which T, = 20000 K, in which the electron-scattering optical depth is less than 1, and in which tbere is significant opacity in the Balmer lines, yields profiles that are much too narrow. In addition, for the parameters deduced by Oke and Sargent for the forbidden-line emitting regions of NGC 4t51, the optical depth in the Balmer lines would be very much less than 1. Fairly good agreement is obtained for an electron temperature of 20000 K and a value of 10 for the optical thickness to electron scattering. Under such conditions, to produce such a profile having the same total luminosity in Hp as that observed in NGC 4151 it is necessary to postulate a small dense region having an electron density of 2.5 X 10 and a dimension of only 0.005 pc. Forbidden lines would be suppressed in this region. We interpret the absorption-line components in the Balmer lines discovered by Anderson and Kraft as evidence for such a dense component. The effects of radiation pressure on material in such a dense region surrounding a small intense source of radiation are significant and might give rise to the observed radial outflow of matter.
R. J. Weymann (Wed,) studied this question.