Optical polarization position angle versus radio structure axis in Seyfert galaxies

Abstract

Optical polarization position angles tend to align with large-scale radio structure in low polarization quasars¹, and they tend to align with or be perpendicular to the radio structure in radio galaxies². In some cases active object emission lines are polarized like the continuum, so the polarization is probably caused by scattering (ref. 3 and R.R.J.A., in preparation). Thus, the polarization alignments indicate the geometrical distribution of scatterers in those cases and so provide information on the matter distribution in the innermost regions. In a new interpretation of the polarization of the Seyfert 2 galaxy NGC1068 (ref. 4), it is noted that the optical polarization of that object is perpendicular to the inner radio contours, while the polarization of the Seyfert 1 galaxy NGC4151 is parallel to the associated radio axis. It is speculated that these are prototypical of two polarization classes of Seyferts analogous to the perpendicular and parallel radio galaxy groups. I show here that this is indeed the case: all Seyfert 1 galaxies in this sample have roughly parallel polarization and all Seyfert 2 galaxies have roughly perpendicular polarizations. These alignment effects can be interpreted as being due to thin and thick scattering disks, respectively, surrounding the continuum sources. This would represent a fundamental difference between the two types of Seyfert galaxies.