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 paper identifies an intermediate line region in AGN's inner torus, showing its evolution from narrow to broad line Seyfert I galaxies and its impact on black hole mass measurements.

Contribution

It provides evidence for an intermediate emission line region in AGNs and explores its evolution and influence on black hole mass estimates.

Findings

Discovery of an intermediate Gaussian component in AGN emission lines.

The intermediate line region (IMLR) is distinct from the very broad line region (VBLR).

Evolution from NLS1s to BLS1s involves changes in the emission line regions.

Abstract

We have decomposed the broad H-alpha, H-beta and H-gamma lines of 90 Active Galactic Nuclei (AGNs) into a superposition of a very broad and an intermediate Gaussian components (VBGC and IMGC) and discovered that the two Gaussian components evolve with FWHM of the whole emission lines. We suggest that the VBGC and the IMGC are produced in different emission regions, namely, Very Broad Line Region (VBLR) and Intermediate Line Region (IMLR). The details of the two components of H-alpha, H-beta and H-gamma lines indicate that the radius obtained from the emission line reverberation mapping normally corresponds to the radius of the VBLR, but the radius obtained from the infrared reverberation mapping corresponding to IMLR, i.e., the inner boundary of the dusty torus. The existence of the IMGC may affect the measurement of the black hole mass in AGNs. Therefore, the deviation of NLS1s from the M-sigma relation may be explained naturally in this way. The evolution of the two emission line regions may be related to the evolutionary stages of the broad line regions of AGNs from NLS1s to BLS1s. Other evidences for the existence of the IMLR are also presented.