Central Masses and Broad‐Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation‐Mapping Database

We present improved black hole masses for 35 active galactic nuclei (AGNs)based on a complete and consistent reanalysis of broad emission-linereverberation-mapping data. From objects with multiple line measurements, wefind that the highest precision measure of the virial product is obtained byusing the cross-correlation function centroid (as opposed to thecross-correlation function peak) for the time delay and the line dispersion (asopposed to full width half maximum) for the line width and by measuring theline width in the variable part of the spectrum. Accurate line-widthmeasurement depends critically on avoiding contaminating features, inparticular the narrow components of the emission lines. We find that theprecision (or random component of the error) of reverberation-based black holemass measurements is typically around 30%, comparable to the precision attainedin measurement of black hole masses in quiescent galaxies by gas or stellardynamical methods. Based on results presented in a companion paper by Onken etal., we provide a zero-point calibration for the reverberation-based black holemass scale by using the relationship between black hole mass and host-galaxybulge velocity dispersion. The scatter around this relationship implies thatthe typical systematic uncertainties in reverberation-based black hole massesare smaller than a factor of three. We present a preliminary version of amass-luminosity relationship that is much better defined than any previousattempt. Scatter about the mass-luminosity relationship for these AGNs appearsto be real and could be correlated with either Eddington ratio or objectinclination.Comment: 61 pages, including 8 Tables and 16 Figures. Accepted for publication in The Astrophysical Journa