2026ApJ...998...60W

The broad-line region (BLR) of active galactic nuclei is an essential component, yet its small size keeps its origin, structure, and kinematics uncertain. Infrared interferometry with VLTI/GRAVITY is now resolving the BLR-scale emission, with data for NGC 3783 consistent with a rotating, geometrically thick configuration. However, the processes shaping the spectra remain poorly constrained, and the cloud models are tuned phenomenologically rather than derived from first-principle predictions. We address this by coupling three-dimensional radiation-hydrodynamic (RHD) simulations of gas around a supermassive black hole with radiative-transfer calculations using CLOUDY, comparing the results to the SINFONI Brγ profile of NGC 3783. We find that Brγ arises from ionized gas in the surface of the rotating thin disk, with electron temperatures of approximately T_e ≈ 10⁴ K and number densities of n_e ≈ 10⁸-10¹¹ cm^–3. However, the intrinsic line profile produced by the RHD kinematics is narrower than observed and displays a substructure. An approximate treatment of the electron scattering suggests that scattering in the surrounding diffuse ionized gas significantly broadens and smooths the intrinsic Brγ profile, making it consistent with the observed profile. This scattering medium has an electron temperature of 10⁴-10⁵ K and a number density of n ≲ 10⁸ cm^–3. Although a best-fit viewing angle of ≈15° is suggested, the scattered line is notably less sensitive to inclination than the intrinsic line. The observed BLR profiles may be understood as the intrinsic emission viewed through an electron-scattering haze, such that some spectral detail is plausibly redistributed rather than seen directly.