Thick turbulent gas disks with magnetocentrifugal winds in active galactic nuclei - Model infrared emission and optical polarization

Abstract

(Abridged) Infrared high-resolution imaging and interferometry have shown that the dust distribution is frequently elongated along the polar direction of an AGN. To explain these findings, we developed a model scenario for the inner ~30 pc of an AGN. We assume a rotating thick gas disk between about one and ten parsec. External gas accretion adds mass and injects energy via gas compression into this gas disk and drives turbulence. Our disks are assumed to be strongly magnetized via equipartition between the turbulent gas pressure and the energy density of the magnetic field. In a second step, we built three dimensional density cubes based on the analytical model, illuminated them with a central source, and made radiative transfer calculations. In a third step, we calculated MIR visibility amplitudes and compared them to available interferometric observations. We show that magneto centrifugal winds starting from a thin and thick gas disk are viable in active galaxy centers. Once the wind is launched, it is responsible for the transport of angular momentum and the gas disk can become thin. The outflow scenario can account for the elongated dust structures, outer edges of the thin maser disks, and molecular outflows observed in local AGN. The models reproduce the observed terminal wind velocities, the scatter of the MIR/intrinsic X-ray correlation, and point source fractions. An application of the model to the Circinus Galaxy and NGC1068 shows that the IR SED, available MIR interferometric observations,and optical polarization can be reproduced in a satisfactory way,provided that (i) a puff-up at the inner edge of the thin disk is present and (ii) a local screen with an optical depth of tau_V 20 inform of a local gas filament and/or a warp of the thick disk hide a significant fraction of both nuclei.

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