Space Telescope and Optical Reverberation Mapping Project. XII. Broad-line Region Modeling of NGC 5548

Abstract

We present geometric and dynamical modeling of the broad line region (BLR) for the multi-wavelength reverberation mapping campaign focused on NGC 5548 in 2014. The data set includes photometric and spectroscopic monitoring in the optical and ultraviolet, covering the Hβ, C IV, and Lyα broad emission lines. We find an extended disk-like Hβ BLR with a mixture of near-circular and outflowing gas trajectories, while the C IV and Lyα BLRs are much less extended and resemble shell-like structures. There is clear radial structure in the BLR, with C IV and Lyα emission arising at smaller radii than the Hβ emission. Using the three lines, we make three independent black hole mass measurements, all of which are consistent. Combining these results gives a joint inference of ( )7.64 10 BH 0.18 0.21 . We examine the effect of using the V band instead of the UV continuum light curve on the results and find a size difference that is consistent with the measured UV-optical time lag, but the other structural and kinematic parameters remain unchanged, suggesting that the V band is a suitable proxy for the ionizing continuum when exploring the BLR structure and kinematics. Finally, we compare the Hβ results to similar models of data obtained in 2008 when the active galactic nucleus was at a lower luminosity state. We find that the size of the emitting region increased during this time period, but the geometry and black hole mass remained unchanged, which confirms that the BLR kinematics suitably gauge the gravitational field of the central black hole.

Reverberation mapping of active galactic nuclei: From X-ray corona to dusty torus

“…(2021) successfully inverted the AGN STORM data for NGC 5548, creating the most detailed velocity-delay maps yet recovered, each one being a projected image along axes of isodelay and line-of-sight velocity for the BLR corresponding to a specific emission line. The velocity-delay maps generally agree with the constraints derived through forward modeling by Williams et al. (2020) , although a disk-like rather than shell-like geometry is preferred for C IV and Lyα.…”

“…Horne et al (2021) successfully inverted the AGN STORM data for NGC 5548, creating the most detailed velocity-delay maps yet recovered, each one being a projected image along axes of isodelay and line-of-sight velocity for the BLR corresponding to a specific emission line. The velocity-delay maps generally agree with the constraints derived through forward modeling by Williams et al (2020), although a disk-like rather than shell-like geometry is preferred for C IV and Lya. There is also evidence in the reverberation response for the presence of an azimuthal structure orbiting on the far side of the C IV and Lya BLR during the monitoring period, as has been seen in several double-peaked AGNs (Gezari et al, 2007;Lewis et al, 2010;Schimoia et al, 2015Schimoia et al, , 2017).…”

“…Coordinated space- and ground-based spectroscopic and photometric monitoring, with a backbone of UV spectroscopy provided by HST , allowed for the most detailed view yet of the BLR and surrounding regions in the AGN NGC 5548. Modeling of the reverberation response across the high- and low-ionization emission lines by Williams et al. (2020) shows that Hβ again arises from a thick disk-like structure.…”

AGN STORM 2. I. First results: A Change in the Weather of Mrk 817

“…The "velocity-delay maps," i.e., the projection of the BLR into the two observables of time delay and line-ofsight velocity, suggest the presence of an inclined disk, but the response of the far side of the disk is weaker than expected (Horne et al 2021). Direct modeling of the spectra yields similar results (Williams et al 2020).…”

Past, Present, and Future of the Scaling Relations of Galaxies and Active Galactic Nuclei

“…The effect can be as large as a factor ≈ 2 and, perhaps more importantly, the efficiency of radiation forces is dependent on the gas column density, leading to the preferential expulsion of gas of lower column density (Netzer and Marziani, 2010). Recent attempts to derive the f S from dynamical models still do not consider the role of radiation pressure on the gas motion (Pancoast et al, 2014a;Pancoast et al, 2014b;Pancoast et al, 2018;Williams et al, 2020). In addition, there are basic difficulties in modeling the BLR.…”