VLT-spectropolarimetry of the high-polarization Seyfert 1 galaxy Fairall 51
Astronomy and Astrophysics
We present high-precision optical spectropolarimetry of the Seyfert 1 galaxy Fairall 51 (F51) taken with FORS1 at the VLT. The observed spectrum shows unpolarized and linearly polarized components. The AGN continuum and the broad lines show (after correction for the Galactic interstellar polarization and the light contribution of the F51 host galaxy) a practically identical amount of intrinsic polarization ranging from 5% in the red to 13% in the UV. The narrow lines are unpolarized or show
... little intrinsic polarization. The observed AGN continuum and the broad line radiation can be explained by a combination of reddened (and attenuated) direct light and scattered light reflected from an optically thin dust region. Hence, within the framework of the unification scheme of AGN, the Seyfert 1 galaxy F51 appears to be an example of a borderline Seyfert 1/Seyfert 2 case where the nucleus is partially obscured like for other type 1 AGN with high intrinsic scattering polarization. It is found that the scattering region in F51 is located far from the BLR and the continuum source. Thanks to this special scattering configuration, we were able to study the kinematics (line profiles) of the broad line region from two different viewing angles, one along the line of sight (in total light) and one via the scattering region (in polarized light). The line profiles in polarized and total light are found to be indistinguishable to a very high accuracy, strongly indicating that the velocity field of the F51 BLR is essentially spherically symmetric.