Evidence for an intermediate line region in AGN's inner torus region and its evolution from narrow to broad line Seyfert I galaxies

TL;DR

This study provides evidence for an intermediate line region in AGN's inner torus, suggesting a two-component model for the broad line region that explains AGN evolution from narrow to broad line Seyfert I galaxies.

Contribution

The paper confirms the two-component BLR model using SDSS data and explores the geometry, density, and evolution of the VBLR and IMLR regions in AGNs.

Findings

Support for the two-component BLR model from SDSS data.

The IMGC affects black hole mass measurements.

Evolution from NLS1s to BLS1s explained by the model.

Abstract

A two-components model for Broad Line Region (BLR) of Active Galactic Nuclei (AGN) has been suggested for many years but not widely accepted (e.g., Hu et al. 2008; Sulentic et al. 2000; Brotherton et al. 1996; Mason et al. 1996). This model indicates that the broad line can be described with superposition of two Gaussian components (Very Broad Gaussian Component (VBGC) and InterMediate Gaussian Component (IMGC)) which are from two physically distinct regions; i.e., Very Broad Line Region (VBLR) and InterMediate Line Region (IMLR). We select a SDSS sample to further confirm this model and give detailed analysis to the geometry, density and evolution of these two regions. Micro-lensing result of 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 broad line regions of AGNs from NLS1s to BLS1s. Based on the results presented here, a unified picture of hierarchical evolution of black hole, dust torus and galaxy is proposed.