EVIDENCE FOR AN INTERMEDIATE LINE REGION IN ACTIVE GALACTIC NUCLEI's INNER TORUS REGION AND ITS EVOLUTION FROM NARROW TO BROAD LINE SEYFERT I GALAXIES

A two-component model for the broad-line region (BLR) of active galactic nuclei (AGNs) has been suggested for many years but not widely accepted. This model indicates that the broad line can be described with the superposition of two Gaussian components (very broad Gaussian component and intermediate Gaussian component (IMGC)) which are from two physically distinct regions, i.e., very broad line region (VBLR) and intermediate line region. We select a Sloan Digital Sky Survey sample to further confirm this model and give a detailed analysis of the geometry, density, and evolution of these two regions. The microlensing result of the BLR in J1131-1231 and some unexplained phenomena in reverberation mapping (RM) experiment provide supportive evidence for this model. Our results indicate that the radius obtained from the emission line RM normally corresponds to the radius of the VBLR, and the existence of the IMGC may affect the measurement of the black hole masses in AGNs. The deviation of NLS1s from the M-sigma relation and the type II AGN fraction as a function of luminosity can be explained in this model in a coherent way. The evolution of the two emission regions may be related to the evolutionary stages of the BLRs of AGNs from NLS1s to BLS1s. Based on the results presented here, a unified picture of the hierarchical evolution of a black hole, a dust torus, and a galaxy is proposed.