Test of the Formation mechanism of the Broad Line Region in Active Galactic Nuclei

TL;DR

This paper investigates the formation mechanisms of the Broad Line Region in active galactic nuclei, comparing two models and finding that the failed dusty outflow model aligns well with observations, unlike the gravitational instability model.

Contribution

It provides a detailed comparison of two proposed BLR formation mechanisms and evaluates their consistency with observational data.

Findings

Failed dusty outflow model matches observed BLR locations.

Self-gravitational instability model is inconsistent with observations.

The reason for the lack of disk instability signatures in BLR remains unclear.

Abstract

The origin of the Broad Line Region (BLR) in active galaxies remains unknown. It seems to be related to the underlying accretion disk but an efficient mechanism is required to rise the material from the disk surface without giving too strong signatures of the outflow in the case of the low ionization lines. We discuss in detail two proposed mechanisms: (i) radiation pressure acting on dust in the disk atmosphere creating a failed wind (ii) the gravitational instability of the underlying disk. We compare the predicted location of the inner radius of the BLR in those two scenarios with the observed position obtained from the reverberation studies of several active galaxies. The failed dusty outflow model well represents the observational data while the predictions of the self-gravitational instability are not consistent with observations. The issue remains why actually we do not see any imprints of the underlying disk instability in the BLR properties.