Broad Emission Line Regions in AGN: the Link with the Accretion Power

Abstract

We present a model which relates the width of the Broad Emission Lines of AGN to the Keplerian velocity of an accretion disk at a critical distance from the central black hole. This critical distance falls in a region bounded on the inward side by the transition radius between the radiation pressure and the gas pressure dominated region of the accretion disk and on the outward side by the maximum radius below which a stabilizing, radially accreting and vertically outflowing corona exists. We show that in the framework of this picture the observed range of H$\beta$ FWHM from Broad Line to Narrow Line type 1 AGN is well reproduced as a function of the accretion rate. This interval of velocities is the only permitted range and goes from $\sim 20,000$ km s$^{-1}$ for sub-Eddington accretion rates, to $\sim 1,000$ km s$^{-1}$ for Eddington accretion rates.