On the Relation between the Inclination Angle of the Accretion Disk and the Broad-line Region in Active Galactic Nuclei

TL;DR

This study investigates the relationship between the inclination angles of the broad-line region and the accretion disk in active galactic nuclei, finding a potential physical alignment supported by observational data.

Contribution

It provides the first robust measurements of accretion disk inclination angles using broadband X-ray reflection spectroscopy and compares them with BLR inclination estimates.

Findings

Strong positive correlation between BLR and disk inclination angles (Pearson 0.856).

Suggests possible physical alignment between the accretion disk and BLR.

Correlation significance is marginal, indicating need for larger sample studies.

Abstract

Models of active galactic nuclei often invoke a close physical association between the broad-line region and the accretion disk. We evaluate this theoretical expectation by investigating the relationship between the inclination angle of the BLR ($\theta_\mathrm{BLR}$) and the inclination angle of the inner accretion disk ($\theta_\mathrm{disk}$). For a sample of eight active galactic nuclei that have published values of $\theta_\mathrm{BLR}$ estimated from dynamical modeling of the BLR based on velocity-resolved reverberation mapping experiments, we analyze high-quality, joint XMM-Newton and NuSTAR X-ray observations to derive new, robust measurements of $\theta_\mathrm{disk}$ through broadband (0.3--78\,keV) reflection spectroscopy. We find a strong, positive correlation between $\theta_\mathrm{BLR}$ and $\theta_\mathrm{disk}$ (Pearson correlation coefficient 0.856, $p$-value 0.007), although Monte Carlo simulations indicate that the level of significance is only marginal ($<3\,\sigma$). Nevertheless, the nearly linear relation between $\theta_\mathrm{BLR}$ and $\theta_\mathrm{disk}$ suggests of a possible physical alignment between the accretion disk and the BLR. Future studies with a larger and more homogeneous sample are needed to confirm the correlation and refine our understanding of the structure and dynamics of the central regions of active galaxies.