The Structure of the Broad-Line Region In Active Galactic Nuclei. II. Dynamical Modeling of Data from the AGN10 Reverberation Mapping Campaign

Abstract: We present inferences on the geometry and kinematics of the broad-Hbeta line-emitting region in four active galactic nuclei monitored as a part of the fall 2010 reverberation mapping campaign at MDM Observatory led by the Ohio State University. From modeling the continuum variability and response in emission-line profile changes as a function of time, we infer the geometry of the Hbeta- emitting broad line regions to be thick disks that are close to face-on to the observer with kinematics that are well-described by either elliptical orbits or inflowing gas. We measure the black hole mass to be log (MBH) = 7.25 (+/-0.10) for Mrk 335, 7.86 (+0.20, -0.17) for Mrk 1501, 7.84 (+0.14, -0.19) for 3C 120, and 6.92 (+0.24, -0.23) for PG 2130+099. These black hole mass measurements are not based on a particular assumed value of the virial scale factor f, allowing us to compute individual f factors for each target. Our results nearly double the number of targets that have been modeled in this manner, and investigate the properties of a more diverse sample by including previously modeled objects. We measure an average scale factor f in the entire sample to be log10(f) = 0.54 +/- 0.17 when the line dispersion is used to characterize the line width, which is consistent with values derived using the normalization of the MBH-sigma relation. We find that the scale factor f for individual targets is likely correlated with the black hole mass, inclination angle, and opening angle of the broad line region but we do not find any correlation with the luminosity.

Overview of Dynamical Modeling of the Broad-Line Region in AGNs

The paper by Grier et al. addresses the structure of the broad-line region (BLR) in active galactic nuclei (AGNs) through a detailed analysis of data from the AGN10 reverberation mapping campaign. It utilizes advanced dynamical modeling techniques to infer the geometry and kinematics of the BLR in four distinct AGNs: Mrk 335, Mrk 1501, 3C 120, and PG 2130+099. This study significantly expands the number of AGNs analyzed using such methods, offering insights into the variability and dynamics of these regions.

Key Findings

1. BLR Geometry and Kinematics: The research models suggest that the BLR in these AGNs can be best described as thick disks that are nearly face-on from the observer's viewpoint. The kinematic behavior of the gas within these regions is described by either elliptical orbits or inflowing gas, indicating that the gravitational dominance of the central supermassive black hole is a key factor in their motion. This aligns with previous interpretations of BLR dynamics using similar modeling techniques.

2. Black Hole Mass Measurements: The study provides estimates for the black hole masses that are independent of the often-assumed virial scale factor ( f ). These measurements are crucial as they directly affect our understanding of the relationship between AGNs and their host galaxies. The masses derived from the models indicate log scales ranging from 6.92 for PG 2130+099 to 7.86 for Mrk 1501.

3. Scale Factor ( f ) and its Implications: The research recalibrates ( f ) by using dynamical modeling, providing distributions of individual ( f ) values for each AGN. The mean scale factors ( \bar{f} ) derived agree with the values typically used in RM-based mass calculations, supporting the validity of previous estimations and reinforcing the importance of accounting for geometric and kinematic variances in individual measurements.

4. Correlation with AGN Properties: The study finds potential correlations between ( f ) and AGN properties such as black hole mass and inclination angles. However, no significant correlation with luminosity or Eddington ratio was observed, suggesting that ( f ) depends more on the intrinsic structure of the BLR rather than the external luminous output of the AGN.

Significance and Future Directions

The paper makes substantial contributions to the field by improving the accuracy of black hole mass estimates through dynamical modeling techniques, which could refine the calibration of the ( M_{\rm BH} - \sigma_* ) relation for AGNs relative to quiescent galaxies. The finding that the modeled geometry and kinematics for AGNs like 3C 120 align with independent measurements (e.g., from radio jet inclination) is particularly noteworthy and may offer new avenues for verifying the orientation of the BLR in other systems.

For future developments, expanding the sample size and including a wider range of AGN types and luminosities would enhance the robustness of these findings. Additionally, comparisons with other reverberation mapping campaigns and integrating complementary observational techniques could provide more comprehensive models of BLR dynamics. The methodology used here also holds potential for application in other astrophysical systems where dynamic modeling can yield significant insights into the underlying physical processes.