Estimating masses of supermassive black holes in active galactic nuclei from the Hα emission line

Aims. The goal of this project is to construct an estimator for the masses of supermassive black holes in active galactic nuclei (AGNs) based on the broad Hα emission line. Methods. We made use of published reverberation mapping data. We remeasured all Hα time lags from the original data as we find that reverberation measurements are often improved by detrending the light curves. Results. We produced mass estimators that require only the Hα luminosity and the width of the Hα emission line as characterized by either the full width at half maximum or the line dispersion. Conclusions. It is possible, on the basis of a single spectrum covering the Hα emission line, to estimate the mass of the central supermassive black hole in AGNs with all three parameters believed to affect mass measurement - luminosity, line width, and Eddington ratio - taken into account. The typical formal accuracy in such estimates is of order 0.2-0.3 dex relative to the reverberation-based masses.