3.3. Orientation, obscuration and AGN Class

The unification scenario that type 2 AGNs are viewed through optically thick material which hides the BELR and the central continuum source is supported statistically by the general tendency for type 2 AGN to have absorbed X-ray spectra (Turner et al. 1997, Awaki et al. 1997), a redder optical continuum, and stronger galactic spectral features. Individual sources are less straight-forward. Optical dust reddening is generally lower than the equivalent X-ray gas absorption (Maiolino et al. 2001, Risaliti et al. 2001). A few sources have been seen to change type, with broad emission lines appearing/disappearing and/or X-ray absorption varying (Matt et al. 2003). Some type 1 or intermediate sources have strong X-ray absorption (Page et al. 2001) and there is little relation between X-ray hardness ratio and AGN class (Wilkes et al. 2002, Figure 5). These results imply a more complex obscuring medium than the optically thick torus originally suggested. Current scenarios generally involve high velocity, accelerating winds originating in a disk (Konigl & Kartje 1994, Murray & Chiang 1995, Konigl this volume, Elvis this volume). These models can also explain the high excitation, broad-absorption lines visible in ~ 10% of type 1 AGN. Variations and differing lines-of-sight to continuum and line regions due to clumpiness and variation in the wind itself can explain the variety of properties seen in individual sources. However to provide real constraints on the structure and geometry of the absorbing material, we need multi-wavelength observations of the intermediate sources discussed above.

Figure 5. X-ray hardness ratios determined by the Chandra for 2MASS red AGN (Wilkes et al. 2002), as a function of optical class demonstrating the lack of a relation between the two in this sample.