Measuring black hole mass of type i active galactic nuclei by spectropolarimetry

Abstract

Black hole (BH) mass of type I active galactic nuclei (AGNs) can be measured or estimated through either reverberation mapping or empirical R-L relation, however, both of them suffer from uncertainties of the virial factor (F BLR ), thus limiting the measurement accuracy. In this letter, we make an effort to investigate F BLR through polarized spectra of the broad-line regions (BLR) arisen from electrons in the equatorial plane. Given the BLR composed of discrete clouds with Keplerian velocity around the central BH, we simulate a large number of spectra of total and polarized flux with wide ranges of parameters of the BLR model and equatorial scatters. We find that the F BLR -distribution of polarized spectra is much narrower than that of total ones. This provides a way of accurately estimating BH mass from single spectropolarimetric observations of type I AGN whose equatorial scatters are identified.