Classification
Seyferts were first classified as Type 1 or 2, depending upon whether the spectra show both narrow and broad emission lines (Type 1), or only narrow lines (Type 2). They are now given a fractional classification depending upon the relative strengths of the narrow and broad components (e.g. Type 1.5 or Type 1.9). It is believed that Type 1 and Type 2 galaxies are in essence the same, and they only differ due to the angle at which they are observed. This is known as Seyfert Unification theory. In Type 2 Seyferts it is believed that the broad component is obscured by dust and/or by our viewing angle on the galaxy. In some Type 2 Seyfert galaxies, the broad component can be observed in polarized light; it is believed that light from the broad-line region is scattered by a hot, gaseous halo surrounding the nucleus, allowing us to view it indirectly. This effect was first discovered by Antonucci and Miller in the Type 2 Seyfert NGC 1068.
Read more about this topic: Seyfert Galaxy