Spectropolarimetry of Seyfert 1 galaxies with equatorial scattering: black hole masses and broad-line region characteristics

Here we present the spectropolarimetric observations of a sample of 30 Type 1 active galactic nuclei (AGNs) and an analysis of the observed polarization in these AGNs. The observations have been performed with the 6 m telescope of SAO RAS using the modified SCORPIO-2 spectropolarimeter. We measured the Stokes parameters for the continuum and the broad H α line and obtained the values of polarization degree and the angle of polarization. We found that equatorial scattering is dominant polarization mechanism in the sample that allows us to use the observed polarization in the broad lines for determination of the central black hole (BH) masses and characteristics (the inclination and emissivity) of the broad-line region (BLR). We demonstrated that the recently proposed method of Afanasiev & Popović (2015) for BH mass measurement gives accurate BH masses that are in a good correlation with the stellar velocity dispersion, and consequently, the masses determined by the polarization method can be used with calibration purposes. Additionally we found that the BLR in the sample of 30 AGNs has an averaged inclination of 35°±9° (mostly between 20° and 40°) and emissivity α ∼ −0.57 that is more flat than one expected for the classical accretion disc α ∼ −0.75.