2015ApJ...802...98M

We propose a new method for estimating the mass of a supermassive black hole, applicable to obscured active galactic nuclei (AGNs). This method estimates the black hole mass using the width of the narrow core of the neutral FeKα emission line in X-rays and the distance of its emitting region from the black hole based on the isotropic luminosity indicator via the luminosity scaling relation. Assuming the virial relation between the locations and the velocity widths of the neutral FeKα line core and the broad Hβ emission line, the luminosity scaling relation of the neutral FeKα line core emitting region is estimated. We find that the velocity width of the neutral FeKα line core falls between that of the broad Balmer emission lines and the corresponding value at the dust reverberation radius for most of the target AGNs. The black hole mass M_BH,FeKα estimated with this method is then compared with other black hole mass estimates, such as the broad emission-line reverberation mass M_BH,rev for type 1 AGNs, the mass M_BH,H2O based on the H₂ O maser, and the single-epoch mass estimate M_BH,pol based on the polarized broad Balmer lines for type 2 AGNs. We find that M_BH,FeKα is consistent with M_BH,rev and M_BH,pol, and find that M_BH,FeKα correlates well with M_BH,H20. These results suggest that M_BH,FeKα is a potential indicator of the black hole mass for obscured AGNs. In contrast, M_BH,FeKα is systematically larger than M_BH,H20 by about a factor of 5, and the possible origins are discussed.