Title: Calibrating Mg ii–based Black Hole Mass Estimators with Hβ Reverberation Measurements
Abstract: Abstract We present the new calibration of black hole mass ( <?CDATA ${M}_{\mathrm{BH}}$?> ) estimators based on the Mg ii λ 2798 broad emission line using the H β reverberation-mapped (RM) sample of 31 active galactic nuclei (AGNs) that have high-quality UV spectra. The updated and enlarged sample at redshift z < 0.16 covers a large dynamic range in <?CDATA ${M}_{\mathrm{BH}}$?> (i.e., <?CDATA ${10}^{5.7}\mbox{--}{10}^{9.0}\,{M}_{\odot }$?> ) and bolometric luminosity (i.e., <?CDATA ${10}^{42.5}\mbox{--}{10}^{46.8}$?> erg s −1 ). We also investigate the mass estimators by adding a sample from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project, which consists of 24 AGNs at a higher redshift range, z = 0.36–0.89. We determine the line width of the Mg ii line using FWHM or line dispersion ( σ line ), which are respectively used for the <?CDATA ${M}_{\mathrm{BH}}$?> recipe. Comparing with the H β reverberation masses, we provide several calibrations for the Mg ii –based mass, the best of which is consistent with the virial assumption and photoionization expectation (i.e., <?CDATA ${M}_{\mathrm{BH}}\propto {L}_{3000}^{0.5}\,{\mathrm{FWHM}}_{\mathrm{Mg}\,{\rm{II}}}^{2}$?> and <?CDATA ${M}_{\mathrm{BH}}\propto {L}_{3000}^{0.5}\,{\sigma }_{\mathrm{Mg}\,{\rm{II}}}^{2}$?> ). The derived <?CDATA ${M}_{\mathrm{BH}}$?> based the Mg ii estimator is consistent with the H β reverberation mass within a factor of 2.