Estimating Black Hole Masses in Active Galaxies Using the Hα Emission Line

It has been established that virial masses for black holes in low-redshift active galaxies can be estimated from measurements of the optical continuum strength and the width of the broad Hβ line. Under various circumstances, however, both of these quantities can be challenging to measure or can be subject to large systematic uncertainties. To mitigate these difficulties, we present a new method for estimating black hole masses. From analysis of a new sample of broad-line active galactic nuclei, we find that Hα luminosity scales almost linearly with optical continuum luminosity and that a strong correlation exists between Hα and Hβ line widths. These two empirical correlations allow us to translate the standard virial mass system to a new one based solely on observations of the broad Hα emission line. Subject headings: galaxies: active — galaxies: jets — galaxies: nuclei — galaxies: Seyfert — quasars: general