Jet Directions in Seyfert Galaxies

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Abstract
Here we present the study of the relative angle between the accretion disk (or radio jet) and the galaxy disk for a sample of Seyfert galaxies selected from a mostly isotropic property, the 60 μm flux, and warm infrared colors. We used VLA A-array 3.6 cm continuum data and ground-based optical imaging, homogeneously observed and reduced to minimize selection effects. For parts of the analysis we enlarged the sample by including galaxies serendipitously selected from the literature. For each galaxy we have a pair of points (i, δ), which are the inclination of the galaxy relative to the line of sight and the angle between the jet projected into the plane of the sky and the host galaxy major axis, respectively. For some galaxies we also had information about which side of the minor axis is closer to Earth. This data is combined with a statistical technique, developed by us, to determine the distribution of β angles in three dimensions, the angle between the jet and the host galaxy plane axis. We found from an initial analysis of the data of the 60 μm sample, where Seyfert 1 and 2 galaxies were not differentiated, that the observed distribution of i and δ values can be well represented either by a homogeneous sin β distribution in the range 0° ≤ β ≤ 90° or in 0° ≤ β ≤ 65°, but not by an equatorial ring. A more general model, which tested β-distributions in the range β1 ≤ β ≤ β2, for different ranges of β1 and β2 values, required β2 to be larger than 65° and gave preference for β1 smaller than 40°-50°. An important result from our analysis was obtained when we determined whether the jet was projected against the near or the far side of the galaxy and differentiated between Seyfert 1 and Seyfert 2 galaxies, which showed that the model could not represent Seyfert 1 galaxies adequately. We found that the inclusion of viewing angle restrictions for Seyfert 1 galaxies, namely, that a galaxy can be recognized as a Seyfert 1 only if the angle between the jet and the line of sight (||) is smaller than a given angle c and that the galaxy inclination i is smaller than an angle ic, gave rise to statistically acceptable models. This indication that there is a difference in viewing angle to the central engine between Seyfert 1 galaxies and Seyfert 2 galaxies is a direct and independent confirmation of the underlying concepts of the unified model. We discuss possible explanations for the misalignment between the accretion disk and the host galaxy disk: warping of the accretion disk by self-irradiation instability, by the Bardeen-Petterson effect, or by a misaligned gravitational potential of a nuclear star cluster surrounding the black hole, as well as feeding of the accretion disk by a misaligned inflow of gas from minor mergers, capture of individual stars or gas from the nuclear star cluster, and the capture of individual molecular clouds from the host galaxy.
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