Polarization and Scattering by Disk-Driven Hydromagnetic Winds in Active Galactic Nuclei

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Session 46 -- Seyfert Galaxies and LINERS
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[46.09] Polarization and Scattering by Disk-Driven Hydromagnetic Winds in Active Galactic Nuclei

J. F. Kartje, A. K\"{o}nigl (U. Chicago)

In a recent investigation, we have shown that centrifugally driven winds originating from the surfaces of magnetized accretion disks may account for many of the spectral characteristics of AGNs and can provide the physical basis for the Seyfert 1/Seyfert 2 unification model. Here, we extend this work to explore the effects of scattering and absorption by gas and dust particles in the wind on photon polarization and the angular dependence of the intensity of the emitted radiation.

There exists convincing evidence that polarized nuclear emission in many Seyfert galaxies and QSOs can be attributed to electron scattering and/or transmission through (or emission by) aligned grains. Both of these mechanisms are expected to play a role in our model: linear polarization will be induced by electron scattering in the hot, inner, ionized regions of the outflow as well as by dust in the cooler, outer wind regions. Polarization will also result from dichroic extinction (or emission) by grains aligned by the magnetic field lines threading the wind. The relative contributions from each mechanism will depend on the field geometry, the dust distribution in the wind, the degree of grain alignment by the magnetic field, and the inclination of the line of sight to the symmetry axis. We have developed a Monte Carlo code to study in detail the predicted polarization patterns as a function of these parameters, and we present preliminary results of this investigation.

Finally, we examine the effects of scattering on the perceived obscuration depths through the wind. We note that radiation scattered into the line of sight could mitigate the effective measured optical depths. This may lead to erroneous conclusions regarding the physical state and geometry of the circumnuclear material, and confusion in determining the critical viewing angle at which the innermost $\sim 1$ pc of the AGN is obscured, thus impairing current attempts to interpret the census of Type 1 and Type 2 sources.

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