Calibrating C-IV-based Black Hole Mass Estimators

Abstract

We present the single-epoch black hole mass estimators based on the C IV λ1549 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 C IV line widths (FWHM_{C IV} and line dispersion, σ_{C IV} ) and the continuum luminosity at 1350 Å (L ₁₃₅₀) 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., M_BH \propto L_{1350}^{0.50+/- 0.07} \sigma _{C\,\scriptsize{IV}}^{2} and M_BH \propto L_{1350}^{0.52+/- 0.09}\,FWHM_{C\,\scriptsize{IV}}^{0.56+/- 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.