| Dr Andy Robinson (Hertfordshire) |
| 13th March 2002 |
| Smoke and Mirrors: probing the nuclear structure of Seyfert galaxies using spectropolarimetry |
| Spectropolarimetry of Type 2 Seyfert nuclei played a key role in establishing the Unification Scheme for Seyfert galaxies in which the broad-line region and continuum source are surrounded by an opaque torus. At first sight, however, the polarization properties of Type 1 Seyferts conflict with this geometry. The results of a spectropolarimetric study of the H-alpha broad emission line in a sample of Seyfert 1s will be presented. Many objects show variations in both degree and position angle of polarization across H-alpha that are best explained by scattering of broad-line emission originating from a rotating disk, by a co-planar scattering region closely surrounding the disk. In contrast, a few objects have polarization spectra characteristic of far-field polar scattering as in Seyfert 2 galaxies in which polarized broad-lines are detected. We propose that the inner scattering region normally dominates the observed polarization of Type 1 Seyferts, but polar scattering dominates when the line-of-sight intercepts the upper layers of the torus. |
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