Spectropolarimetry of Seyfert 1 galaxies with equatorial scattering: Black hole masses and Broad Line Region characteristics

TL;DR

This study uses spectropolarimetry of 30 Seyfert 1 galaxies to determine black hole masses and Broad Line Region characteristics, confirming the effectiveness of polarization-based measurements and revealing typical BLR inclinations and emissivity profiles.

Contribution

It introduces a polarization-based method for measuring black hole masses and BLR properties in Seyfert 1 galaxies, validated against stellar velocity dispersions.

Findings

Equatorial scattering dominates polarization in the sample.

Black hole masses correlate well with stellar velocity dispersions.

BLR inclination averages around 35 degrees with a flatter emissivity profile.

Abstract

Here we present the spectropolarimetric observations of a sample of 30 Type 1 AGNs and an analysis of the observed polarization in these AGNs. The observations have been performed with the 6-meter telescope of SAO RAS using the modified SCORPIO-2 spectropolarimeter. We measured the Stokes parameters for the continuum and the broad H$\alpha$ 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 \cite{ap15} for BH mass measurement gives accurate BH masses which 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 AGN has an averaged inclination of $35^\circ\pm9^\circ$ (mostly between 20 and 40 degrees) and emissivity $\alpha\sim -0.57$ that is more flat than one expected for the classical accretion disc $\alpha\sim -0.75$.