Spectropolarimetry and the structure of active galactic nuclei
Previous work on polarized Seyfert galaxies has shown that type 1's have their optical continuum polarization aligned with the nuclear radio structure, while type 2's have a perpendicular relationship between these two features. Radio galaxies also show a bimodal distribution in this relationship, while all low polarization QSOs show a parallel orientation. Polarized Seyfert 2 galaxies tend to have a relatively higher polarization that is wavelength independent. Five out of ten type 2's we have observed have a highly obscured type 1 component that is revealed by the polarization measurements. We interpret this in terms of an obscuring torus which hides our direct view of the type 1 region and continuum source; these are made visible by scattering by electrons located above and below the torus. This is confirmed by the discovery of three offnuclear regions in NGC 1068 which contain dusty regions that reflect light from the hidden region and allow multidirectional views of the nucleus. These data can be fit by a model consisting of a highly ionized wind flowing in a conical pattern which reflects the type 1 region including the x-ray continuum.
Seyfert 1's generally have low polarizations with varied origins, but the data are consistent with type 1's containing relatively thin disks that do not obscure the central regions. An alternative picture is that type 1's and 2's are the same kind of objects, but differ primarily in viewing aspect; this picture has several problems. Low polarization QSOs appear to be closely related in polarization properties to Seyfert 1's, and the non-variable high polarization QSO OI 287 may be an example of thin disk that is seen nearly edge on.
KeywordsRadio Source Thin Disk Radio Galaxy Broad Line Direct View
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