Polarization of broad line emission in radio galaxies

Abstract

We present the results of our estimations of the polarization degree of broad line emission for the radio galaxies 3C 120, Mrk 335, Mrk 1501, and PG 2130 + 099. We derived the polarization degree for every broad line of 3C 120: Hα, Hβ, Hγ, and HeIλ5876 using the published data for the geometrical parameters and the structure of the broad line region (BLR) of 3C 120. We used published estimates of the geometrical thickness to the radius ratio for every broad emission line. The estimated vertical BLR structure corresponds to the disk‐like structure of this region in active galactic nuclei (AGN). Also for objects Mrk 335, Mrk 1501, and PG 2130 + 099, we estimated the polarization degree using inclination angle values from the literature. As a result, measuring the polarization degree of broad line emissions acquires the central meaning for determination of the geometrical parameters of the BLR in AGN.

Polarization in broad emission lines of active galactic nuclei

“…It seems that the (PA), in the case of the Keplerian motion in combination with equatorial scattering could be used for the SMBH estimates. First of all, one can expect in the case of rotation motion caused by gravitation, the PA should have a swing in the profile across the broad lines (see models in Piotrovich et al 2019; Savić et al 2018, 2020). This is caused by the equatorial scattering of radial component velocity component.…”

“…The line width measured in the polarized flux overcomes the inclination bias and provides a close‐to equatorial view of the BLR in all AGN, which allows to reduce the inclination bias in the BLR based black hole mass estimates (Piotrovich et al 2019).…”