DISK-DRIVEN HYDROMAGNETIC WINDS AS A KEY INGREDIENT OF ACTIVE GALACTIC NUCLEI UNIFICATION SCHEMES

Centrifugally driven winds from the surfaces of magnetized accretion d isks have been recognized as an attractive mechanism of removing the a ngular momentum of the accreted matter and of producing the bipolar ou tflows and jets that are often associated with compact astronomical ob jects. As previously suggested in the context of young stellar objects , such winds have unique observational manifestations stemming from th eir highly stratified density and velocity structure and from their ex posure to the strong continuum radiation field of the compact object. We have applied this scenario to active galactic nuclei (AGNs) and inv estigated the properties of hydromagnetic outflows that originate with in approximately 10M8 pc of the central 10(8)M(8) M. black hole. On th e basis of our results, we propose that hydromagnetic disk-driven wind s may underlie the classification of broad-line and narrow-line AGNs ( e.g., the Seyfert 1/Seyfert 2 dichotomy) as well as the apparent deart h of luminous Seyfert 2 galaxies. More generally, we demonstrate that such winds could strongly influence the spectral characteristics of Se yfert galaxies, QSOs, and BL Lac objects (BLOs). According to the Seyf ert unification scheme, Seyfert 2 galaxies represent Seyfert 1 galaxie s that are obscured by a dusty torus. Analogous schemes have been prop osed for relating narrow-line radio galaxies to broad-line radio galax ies and radio-loud QSOs, and luminous QSOs to ultraluminous infrared g alaxies. In our picture, the torus is identified with the outer region s of the wind where dust uplifted from the disk surfaces by gas-grain collisions is embedded in the outflow. Using an efficient radiative tr ansfer code, we show that the infrared emission of Seyfert galaxies an d QSOs can be attributed to the reprocessing of the UV/soft X-ray AGN continuum by the dust in the wind and the disk. We demonstrate that th e radiation pressure force flattens the dust distribution in objects w ith comparatively high (but possibly sub-Eddington) bolometric luminos ities, and we propose this as one likely reason for the apparent pauci ty of narrow-line objects among certain high-luminosity AGNs. Using th e XSTAR photoionization code, we show that the inner regions of the wi nd could naturally account for the warm (greater than or similar to 10 (5) K) and hot (greater than or similar to 10(6) K) gas components tha t have been inferred to exist on scales lesser than or similar to 10(2 ) pc in several Seyfert galaxies. We suggest that the partially ionize d gas in the inner regions of the wind, rather than the dusty, neutral outflow that originates further out in the disk, could account for th e bulk of the X-ray absorption in Seyferts observed at relatively smal l angles to their symmetry axes. Electron scattering by this gas might give rise to the ''ionization cones'' that have been detected in obje cts like NGC 1068 (with a corresponding focusing of the X-ray emission possibly contributing to the apparent deficit of X-ray-luminous Seyfe rt 2 galaxies), and it could also be responsible for some of the conti nuum optical polarization chaacteristics of Seyfert galaxies and radio -quiet QSOs. Other observed optical and infrared polarization properti es of these AGNs may be attributed to the effects of dust scattering a nd transmission in the outer zones of the wind. Finally, we discuss th e application of this model to the interpretation of the approximately 0.6 keV X-ray absorption feature reported in several BLOs.