Calibrating CIV-based black hole mass estimators
  We present the single-epoch black hole mass estimators based on the CIV (1549
A) broad emission line, using the updated sample of the reverberation-mapped
AGNs and high-quality UV spectra. By performing multi-component spectral
fitting analysis, we measure the CIV line widths (FWHM_CIV) and line dispersion
(sigma_CIV) and the continuum luminosity at 1350 A (L_1350) to calibrate the
CIV-based mass estimators. By comparing with the Hbeta reverberation-based
masses, we provide new mass estimators with the best-fit relationships, i.e.,
M_BH \propto L_1350 ^ (0.50+-0.07) sigma_CIV ^2 and M_BH \propto L_1350 ^
(0.52+-0.09) FWHM_CIV ^ (0.56+-0.48). The new CIV-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.
