Spectral energy distributions of Seyfert nuclei

We present nuclear spectral energy distributions (SEDs) in the range 0.4-16 mum for an expanded CfA sample of Seyfert galaxies. The spectral indexes (f(nu) proportional to nu(-alphaIR)) from 1 to 16 mum range from alpha(IR) similar to 0.9 to 3.8. The shapes of the spectra are correlated with Seyfert type in the sense that steeper nuclear SEDs (nuf(nu) increasing with increasing wavelength) tend to be found in Seyfert 2's, and flatter SEDs (nuf(nu) is constant) in Seyfert 1-1.5's. The galaxies optically classified as Seyferts 1.8's and 1.9's display values of alpha(IR) as in type 1 objects, or values intermediate between those of Seyfert 1's and Seyfert 2's. The intermediate SEDs of many Seyfert 1.8-1.9's may be consistent with the presence of a pure Seyfert 1 viewed through a moderate amount (A(V) less than or similar to 5 mag) of foreground galaxy extinction. We find, however, that between 10% and 20% of galaxies with broad optical line components have steep infrared SEDs. Torus models usually adopt high equatorial opacities to reproduce the infrared properties of Seyfert 1's and 2's, resulting in a dichotomy of infrared SEDs (flat for type 1's, and steep for type 2's). Such a dichotomy, however, is not observed in our sample. The wide range of spectral indexes observed in the type 2 objects, the lack of extremely steep SEDs, and the large numbers of objects with intermediate spectral indexes cannot be reconciled with predictions from existing optically thick torus models. We discuss possible modifications to improve torus models, including low optical depth tori, clumpy dusty tori, and high optical depth tori with an extended optically thin component.