Estimating Black Hole Masses in Active Galaxies Using the Halpha Emission Line
Jenny E. Greene, Luis C. Ho
TL;DR
The paper introduces a novel method to estimate supermassive black hole masses in active galactic nuclei using only broad Hα emission, motivated by difficulties measuring the traditional L5100 continuum or Hβ in some sources. It establishes two key empirical correlations: L_Hα scales with L5100, and FWHM_Hα tracks FWHM_Hβ, enabling a virial mass formalism based solely on Hα. The authors derive explicit M_BH estimators from L_Hα and FWHM_Hα and compare them with Kaspi 2005 results, showing consistency and extending applicability to jet-dominated and low-luminosity AGNs. They discuss implications for BLR physics (Balmer decrement, line widths) and note potential biases for highly beamed radio-loud objects.
Abstract
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 Hbeta 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 Halpha luminosity scales almost linearly with optical continuum luminosity and that a strong correlation exists between Halpha and Hbeta 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 Halpha emission line.