Modelling the AGN broad line region using single-epoch spectra II. Nearby AGN

TL;DR

This paper presents a Bayesian single-epoch spectral model for the broad line region in AGN, enabling estimation of BLR properties with limited data, thus facilitating studies of black hole masses across diverse AGN populations.

Contribution

It introduces a new Bayesian physical model that infers BLR geometry and dynamics from single-epoch spectra, validated against monitoring data, and applicable to large AGN samples.

Findings

Model constrains BLR parameters consistent with monitoring data.

Stronger constraints for AGN with complex emission line structures.

Practical tool for high-redshift and large-sample AGN studies.

Abstract

The structure of the broad line region (BLR) is an essential ingredient in the determination of active galactic nuclei (AGN) virial black hole masses, which in turn are important to study the role of black holes in galaxy evolution. Constraints on the BLR geometry and dynamics can be obtained from velocity-resolved studies using reverberation mapping data (i.e. monitoring data). However, monitoring data are observationally expensive and only available for a limited sample of AGN, mostly confined to the local Universe. Here we explore a new version of a Bayesian inference, physical model of the BLR which uses an individual spectrum and prior information on the BLR size from the radius-luminosity relation, to model the AGN BLR geometry and dynamics. We apply our model to a sample of 11 AGN, which have been previously modelled using monitoring data. Our single-epoch BLR model is able to constrain some of the BLR parameters with inferred parameter values that agree within the uncertainties with those determined from the modelling of monitoring data. We find that our model is able to derive stronger constraints on the BLR for AGN with broad emission lines that qualitatively have more substructure and more asymmetry, presumably as they contain more information to constrain the physical model. The performance of this model makes it a practical and cost-effective tool to determine some of the BLR properties of a large sample of low and high redshift AGN, for which monitoring data are not available.