Models of the continuum polarization in active galactic nuclei: Implications for unification schemes

I have computed the UBV RI-band thermal continuum polarization induced by gas and dust arranged in configurations compatible with current active galactic nuclei (AGNs) unification schemes. Both uniform-density tori and stratified-density disk-driven winds were considered. A Monte Carlo radiative transfer code was developed which includes the polarization mechanisms of electron and dust scattering as well as dichroic extinction by aligned grains. I propose a new interpretation of many of the observed polarization traits of Seyfert galaxies and QSOs: namely, that the polarization in these sources is induced by the same optically thick material which is assumed to obscure the central engine in unification schemes.; Stratified-density winds could provide a natural explanation of the polarization trends observed in Seyfert galaxies. Such winds display polarizations ({dollar}P sbsp{lcub}sim{rcub}{lcub}<{rcub}{dollar} 15%) oriented perpendicular to the axis along viewing angles inclined to the axis by {dollar}thetasb{lcub}o{rcub} sbsp{lcub}sim{rcub}{lcub}>{rcub}{dollar} 45{dollar}spcirc{dollar}; this polarization shifts to smaller magnitudes ({dollar}P sbsp{lcub}sim{rcub}{lcub}<{rcub}{dollar} 2%) and parallel orientations for more face-on viewing, consistent with the patterns observed in Seyfert 2 and Seyfert 1 sources, respectively. Simple torus models cannot produce these viewing angle-dependent changes in P and the position angle.; The magnitude of P depends on the opening angle and optical depth of the torus or wind, the degree of grain alignment, and the location of the continuum source within the obscuring material. The polarization position angle is defined by the primary photon scattering planes within the gas and dust and the direction of grain alignment. It may be oriented either perpendicular or parallel to the symmetry axis, or along an intermediate angle determined by the grain alignment. {dollar}P(lambda{dollar}) may rise into the blue, rise into the red, or remain roughly constant depending on the torus/wind optical depth, degree of grain alignment, and viewing angle.; I also consider the collimation of the central continuum emission by the obscuring dust and gas. I show that disk-driven winds are effective collimators which can produce apparent cones of ionizing photons even though they lack the sharp edges of uniform-density tori.