Calibrating Mg II-based Black Hole Mass Estimators with Hβ Reverberation Measurements

We present the new calibration of black hole mass (M-BH) estimators based on the Mg II lambda 2798 broad emission line using the H beta 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(9.0)M(circle dot)) 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 (sigma(line)), which are respectively used for the M-BH recipe. Comparing with the H beta reverberation masses, we provide several calibrations for the Mg IT-based mass, the best of which is consistent with the virial assumption and photoionization expectation (i.e., M-BH alpha L-3000(0.5) FWHMMg II2 and M-BH alpha L-3000(0.5) sigma(Mg) (2)(II)). The derived M-BH based the Mg II estimator is consistent with the H beta reverberation mass within a factor of 2.