THE FUNDAMENTAL PLANE OF THE BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI

Abstract

Broad emission lines in active galactic nuclei (AGNs) mainly arise from gas photoionized by continuum radiation from an accretion disk around a central black hole. The shape of the broad-line profile, described by , the ratio of full width at half maximum to the dispersion of broad H β , reflects the dynamics of the broad-line region (BLR) and correlates with the dimensionless accretion rate ( ) or Eddington ratio ( / ). At the same time, and / correlate with , the ratio of optical Fe ii to H β line flux emission. Assembling all AGNs with reverberation mapping measurements of broad H β , both from the literature and from new observations reported here, we find a strong bivariate correlation of the form where α  = (2.47, 0.31), β  = −(1.59, 0.82), and γ  = (1.34, 0.80). We refer to this as the fundamental plane of the BLR. We apply the plane to a sample of z  < 0.8 quasars to demonstrate the prevalence of super-Eddington accreting AGNs are quite common at low redshifts.