CALIBRATING C-IV-BASED BLACK HOLE MASS ESTIMATORS.

We present the single-epoch black hole mass estimators based on the C IV λ 1549 broad emission line, using the updated sample of the reverberation-mapped active galactic nuclei and high-quality UV spectra. By performing multi-component spectral fitting analysis, we measure the Civ line widths (FWHMC IV and line dispersion, σC IV) and the continuum luminosity at 1350 Å (L1350) to calibrate the C-IV-based mass estimators. By comparing with the Hβ reverberation-based masses, we provide new mass estimators with the best-fit relationships, i.e., MBH α L13500.50±0.07 σC IV2 and MBH α L13500.52±0.09 FWHMC IV0.56±0.48. The new C-iv-based mass estimators show significant mass-dependent systematic difference compared to the estimators commonly used in the literature. Using the published Sloan Digital Sky Survey QSO catalog, we show that the black hole mass of high-redshift QSOs decreases on average by ~0.25 dex if our recipe is adopted. [ABSTRACT FROM AUTHOR]