2019ApJ...875...50B

We present the new calibration of black hole mass (M_BH) estimators based on the Mg II λ2798 broad emission line using the Hβ 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 M_BH (i.e., 10^5.7–10^9.0M_☉) and bolometric luminosity (i.e., 10^42.5–10^46.8 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 M_BH recipe. Comparing with the Hβ 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., M_BH∝L₃₀₀₀^0.5FWHM_MgII² and M_BH∝L₃₀₀₀^0.5σ_MgII²). The derived M_BH based the Mg II estimator is consistent with the Hβ reverberation mass within a factor of 2.