SPECTROPOLARIMETRY OF HIGH-POLARIZATION SEYFERT-1 GALAXIES - GEOMETRY AND KINEMATICS OF THE SCATTERING REGIONS

We present moderate-resolution (10 Angstrom) spectropolarimetry of nine Seyfert 1 galaxies. Four of the objects are either essentially unpolarized (NGC 6212 and NGC 7469) or polarized by interstellar dust in our own Galaxy (III Zw 2 and NGC 6814). The most striking result for the remainder is that all of them show emission-line polarization and show evidence for multiple sources of polarization. Some objects appear to be polarized by dust reflection, others by electron scattering, and at least one by both. These observations rule out simple, axisymmetric models of the Seyfert nuclei and their immediate environment. The high polarization of Mrk 231 results from light reflected by high-velocity dust clouds. We find that the H alpha emission line is redshifted in polarized flux by 600 km s(-1), implying outflowing dust. Since the polarization position angle of 98 degrees is perpendicular to the radio axis (9 degrees), the outflow must be along the axis of symmetry of the system. The rotation of position angle with wavelength is caused by differing emission-line and continuum polarizations, and their changing relative contributions with wavelength. The new absorption system reported by Boroson et al. (1991) is visible in our spectra, and we confirm the variability curve of this feature reported by Kollatschny et al. (1992). The spectral polarization structures of Mrk 376 and Mrk 704 are quite similar. The blue continuum seen in polarized flux argues for dust scattering as the polarization mechanism. Small rotations in position angle across the broad line profiles are seen. In both Mrk 509 and NGC 5548 the H alpha lines appear broader in polarized flux than in total flux, with P rising above the continuum P in the far wings. A position angle rotation in Mrk 509 argues for two polarization sources, possibly one blueshifted and the other redshifted, explaining the line broadening. We argue that in NGC 5548 the broadening is caused by electron scattering, the hot electrons Doppler-broadening the emission line by their thermal velocities. NGC 5548 also shows evidence for a second, orthogonally polarized component of Ha, narrower than the first, and blueshifted. The dominant component is polarized perpendicularly to the axis defined by the 3.6 cm VLA radio map. We have proposed that Seyfert 1 galaxies and quasars are polarized by scattering preferentially in the plane of a relatively thin disk. Simple models of scattering from an equatorial disk predict maximum polarizations of less than or equal to 7% when the central source is seen directly. This is consistent with the polarizations seen in most high-P Seyfert 1's (P approximate to 5%-6%). Mrk 231 is clearly a different case in which the continuum source is reddened, and the scattering occurs along the axis of symmetry rather than the equatorial plane. The simple models indicate the presence of material concentrated toward the equatorial planes of high-P Seyfert 1's, as would be expected from ''unified'' theories of Seyfert galaxies. In these theories Seyfert 2's are actually Seyfert 1's with their broad-line regions obscured from direct view. The two orthogonally polarized components of NGC 5548 may represent the two regions predicted to be present: an optically thick equatorial disk and an optically thin cone-shaped scattering region. However, the variety of effects seen in the polarization spectra of the Seyfert 1's studied show that these simple models are not sufficient to explain the details observed.