Spectropolarimetry of high-polarization Seyfert 2 galaxies and unified Seyfert theories

Abstract

We have used spectropolarimetry to study eight high-polarization Seyfert 2 galaxies and find in four of them (Mrk 3, Mrk 348, Mrk 463E, and NGC 7674) evidence for a hidden broad-line region (BLR), visible only in the polarized flux spectrum. The other four objects, Mrk 78, Mrk 1066, NGC 591, and NGC 7672, may also have hidden BLRs, but at a flux level below our detection threshold. The properties of the hidden BLRs are consistent with their being normal Seyfert 1 nuclei. If all Seyfert 2 galaxies are in reality Seyfert 1 galaxies in which the nuclei are hidden from direct view and seen only in scattered light, then one might expect that many Seyfert 2 galaxies have polarizations of their featureless continua greater than 50%. Such high polarizations are not seen, perhaps indicating a particular geometry, in which nearly edge-on obscuring tori also block light from the scattering region. This model predicts that in edge-on cases we will detect little or no featureless continua in the spectra of the objects. We present arguments that objects with high luminosity, such as QSOs, have geometrically thin tori and hence are much less likely to have obscured continua and BLRs.