Modeling reverberation mapping data I: improved geometric and dynamical models and comparison with cross-correlation results

TL;DR

This paper introduces an improved phenomenological model for the broad line region in active galactic nuclei, enabling direct reverberation mapping data modeling to better constrain black hole mass and BLR geometry, and compares it with traditional cross-correlation methods.

Contribution

The paper develops an enhanced BLR model that allows direct data fitting, improving black hole mass estimates and understanding of BLR structure beyond prior indirect methods.

Findings

Black hole mass can be recovered with 0.05-0.25 dex uncertainty.

The model distinguishes between elliptical and inflowing gas dynamics.

Uncertainty in black hole mass measurement is around 0.25 dex.

Abstract

We present an improved and expanded simply parameterized phenomenological model of the broad line region (BLR) in active galactic nuclei (AGN) for modeling reverberation mapping data. By modeling reverberation mapping data directly, we can constrain the geometry and dynamics of the BLR and measure the black hole mass without relying on the normalization factor needed in the traditional analysis. For realistic simulated reverberation mapping datasets of high-quality, we can recover the black hole mass to $0.05-0.25$ dex uncertainty and distinguish between dynamics dominated by elliptical orbits and inflowing gas. While direct modeling of the integrated emission line light curve allows for measurement of the mean time lag, other details of the geometry of the BLR are better constrained by the full spectroscopic dataset of emission line profiles. We use this improved model of the BLR to explore possible sources of uncertainty in measurements of the time lag using cross-correlation function (CCF) analysis and in measurements of the black hole mass using the virial product. Sampling the range of geometries and dynamics in our model of the BLR suggests that the theoretical uncertainty in black hole masses measured using the virial product is on the order of 0.25 dex. These results support the use of the CCF to measure time lags and the virial product to measure black hole masses when direct modeling techniques cannot be applied, provided the uncertainties associated with the interpretation of the results are taken into account.