The nature of the ultraviolet continuum in type 2 Seyfert galaxies
Type 2 Seyfert nuclei are well known to contain a “featureless continuum” which makes a significant contribution in the optical and ultraviolet. However, the nature of this featureless continuum is not clear. Optical spectropolarimetry shows that only a minor part of the optical featureless continuum can be light from a hidden Seyfert 1 nucleus scattered into the line of sight. The authors show that this is also true in the ultraviolet. The authors have used International Ultraviolet Explorer spectra of 20 of the brightest type 2 Seyfert nuclei to construct an ultraviolet spectral template. While the continuum is well detected in the template, there is no detectable broad-line region (BLR). Comparing this template to a similar spectral template of type 1 Seyfert nuclei implies that no more than 20% of the Seyfert 2 template's continuum can be light from a hidden Seyfert 1 nucleus scattered by dust or warm electrons. One obvious possibility is that most of the nuclei in the sample are “pure” type 2 Seyfert galaxies that do not contain a hidden type 1 Seyfert nucleus (e.g. there is a clear view of the central engine in the ultraviolet, and it simply lacks a BLR). This is not compatible with the evidence that at least some Seyfert 2 galaxies can be unified with Seyfert 1 galaxies on the basis of viewing geometry, unless there are two types of Seyfert 2 galaxies
