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2.4. Intermediate Type Seyferts

Very likely, the obscuring torus has both a Compton thick parsec-scale component and a larger 100 pc-scale component which is coplanar with the galactic disk and characterized by lower NH (which does not violates the mass constraints). The internal torus obscures completely the BLR along the intercepting lines of sight (Sy2 case), while the obscuration due to the external torus (in edge-on systems) is moderate and the Seyfert nucleus might show weak broad lines and, therefore, might be classified as intermediate type 1.8-1.9. Indeed, intermediate type Sys are more commonly found in edge-on galaxies (Maiolino & Rieke 1995). This model is also supported by the distribution of absorbing column of intermediate Seyferts, which is significantly shifted towards lower values of NH than strict Sy2s (Risaliti et al. 1999, Fig. 1). Although, this model might apply to many intermediate type Seyferts, there are Seyfert galaxies whose intermediate properties are not to ascribe to moderate obscuration but to photoionization and variability effects or to more complex forms of absorption (Goodrich et al. 1995, Komossa & Fink 1997).