A Link between the Hβ Equivalent Width, Profile Width, BLR Size, and Optical Luminosity from a Small Sample of Well-studied Active Galactic Nuclei

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Abstract

We present diagrams of the relationship between the broad Hβ emission-line parameters and the continuum luminosity obtained from a sample of 31 well-studied Seyfert 1.0–1.5 galaxies and quasars. The equivalent width of the Hβ line is inversely correlated with the continuum luminosity at 5100 Å as EW ∼ L, which seems to be comparable to that obtained by other authors for the Lyα. So, we have detected, although very marginally, a Baldwin effect in the Hβ line. The remarkably small scattering of the Hβ equivalent widths probably indicates approximately the same spectral energy distribution from optics to ionizing radiation, nearly the same covering factor, and nearly isotropic continuum emission, although some of these agents can show small systematic changes with luminosity. The intrinsic Baldwin effect for the Hβ is clearly seen only in NGC 5548. Considering the observed lag-luminosity and lag–line-width dependences we suppose that it might be caused by full ionization of clouds. We compute the linear regression parameters (the slopes and intercepts) of the relationship between the Hβ and optical continuum fluxes. In some cases, the regression parameters derived from the homogeneous data sets are significantly different for different observational periods. The lag of the Hβ response to continuum variations shows a strong correlation with the luminosity. Combining the regression results on time delay and rms widths of the Hβ line, we obtained the following mass-luminosity relationship for AGNs: L ∝ M1.9±1.1.

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