Extending the Calibration of C iv-based Single-epoch Black Hole Mass Estimators for Active Galactic Nuclei*

Abstract

Abstract We provide an updated calibration of C iv λ 1549 broad emission line–based single-epoch (SE) black hole (BH) mass estimators for active galactic nuclei (AGNs) using new data for six reverberation-mapped AGNs at redshift z = 0.005 – 0.028 with BH masses (bolometric luminosities) in the range 10 6.5 – 10 7.5 M ⊙ ( 10 41.7 – 10 43.8 erg s−1). New rest-frame UV-to-optical spectra covering 1150–5700 Å for the six AGNs were obtained with the Hubble Space Telescope (HST). Multicomponent spectral decompositions of the HST spectra were used to measure SE emission-line widths for the C iv, Mg ii, and Hβ lines, as well as continuum luminosities in the spectral region around each line. We combine the new data with similar measurements for a previous archival sample of 25 AGNs to derive the most consistent and accurate calibrations of the C iv-based SE BH mass estimators against the Hβ reverberation-based masses, using three different measures of broad-line width: full width at half maximum (FWHM), line dispersion ( σ line ), and mean absolute deviation (MAD). The newly expanded sample at redshift z = 0.005 – 0.234 covers a dynamic range in BH mass (bolometric luminosity) of log M BH / M ☉ = 6.5 – 9.1 ( log L bol / erg s−1 = 41.7 – 46.9 ), and we derive the new C iv-based mass estimators using a Bayesian linear regression analysis over this range. We generally recommend the use of σ line or MAD rather than FWHM to obtain a less biased velocity measurement of the C iv emission line, because its narrow-line component contribution is difficult to decompose from the broad-line profile.