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Spectrophotometric measurements show five galaxies with strong narrow emission lines combined with weak, broad H-alpha and H-beta components to have line and continuum spectral properties intermediate between those of Seyfert 1 and Seyfert 2 galaxies. Because they are closer to the latter, they are called Seyfert 1.8 and Seyfert 1.9, depending on the presence of broad H-beta emissions in the scans. The observed intensity ratios of the broad H-alpha/H-beta emission lines are large compared with those of typical Seyfert 1 galaxies, suggesting the importance of dust in the broad-line regions. Narrow-line spectra of the Seyfert 1.8 and 1.9 are found to have low ionization, implying that their narrow-line region is reached by few high-energy photons. Emphasis is placed on the correlation between a strong, featureless continuum and broad H I emission lines in Seyfert and radio galaxies.
Donald E. Osterbrock (Thu,) studied this question.