Abstract We analyzed a large sample of Sloan Digital Sky Survey spectra of Seyfert galaxies, subdividing type 1 Seyferts (Sy1s) based on their narrow to broad H α components. Comparing their narrow lines (NLs) to type 2 Seyferts (Sy2s) in line-ratio diagrams, most of the NLs of strong Sy1.0/Sy1.2s (with dominant broad lines) are the same as those of “pure” Sy2s. In contrast, only ∼25%–30% of the Sy1.8 and Sy1.9 nuclei (with weak broad lines) are located in the pure Sy2 region, with the rest falling in the composite/star-forming region. We explain these Seyfert+star formation spectra with a simple model. It shows that 85% of NLs in Sy1.9s are from H II regions, while 88% of the NLs in Sy1.0s arise from the same narrow-line region as in pure Sy2s. About ∼6% of the strong and weak Sy1s have NLs dominated by low-ionization nuclear emission-line region (LINER) emission, while ∼15% of intermediate Seyferts (Sy1.5/Sy1.6) do. To confirm this Seyfert 1 active galactic nucleus (AGN)+star formation combination, we used stellar absorption lines to compare their stellar populations. Their H δ strengths show that LINERs, pure Sy2s, and also the broad-line-dominated Sy1s have old stellar populations. The weak Sy1s show stronger H δ absorption, indicating larger proportions of young stars. About one-third of the u -band light in Sy1.0/1.2s is blended Balmer lines and continuum from the broad-line region (BLR). The NL gas reddening increases as the BLR strength decreases, from Sy1.0 (0.13 mag) to Sy1.9 (0.40 mag), to Sy2s and LINERs, both with 0.50 mag. Our data do not support the simplest version of Seyfert 1 and 2 unification, where both AGN classes have identical NLs.
Malkan et al. (Tue,) studied this question.