Broad Line Regions behind a Haze II: A Three-dimensional Electron-scattering Model of the Broad Brγ Line in NGC 3783
Abstract
We investigate the broad Brγ line in the type-1 active galactic nucleus NGC 3783 using three-dimensional Monte Carlo electron-scattering radiative transfer with SKIRT. Paper-I reproduced the observed smooth core and broad wings by convolving an intrinsic Keplerian profile with the analytic electron-scattering kernel of Laor (2006). Here we instead transport photons through explicit source and scattering geometries. For a partially covered Keplerian source, three-dimensional transfer broadens only the scattered photons and leaves an unscattered double-peaked core. For the thin Keplerian source motivated by Paper-I, a comparison of four scattering-geometry classes shows that neither a disk-like scatterer nor the tested halo variants reproduce both the core and wings. We therefore construct a two-component-source (2CS) model containing an inner Keplerian source disk, a rotating disk haze, a nearly spherical halo haze, and direct emission from a slower outer disk. A reference 2CS calculation gives Xi^2 =1.154 at i=15 deg. Polar cones with an input radial optical depth tau_hole=0.1 preserve the line profile and give a measured Thomson-thin sightline. The preferred low redistribution width, full-column ionization, and weak recombination emission cannot all be realized by a uniform thermal halo. The 2CS model is therefore a physically motivated parametric description whose medium must ultimately be tested with self-consistent radiative transfer, ionization, and dynamics.
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BibTeX
@misc{wada2026broad,
title = {{Broad Line Regions behind a Haze II: A Three-dimensional Electron-scattering Model of the Broad Br$γ$ Line in NGC 3783}},
author = {Keiichi Wada and Bert Vander Meulen},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.23368},
eprint = {2610.23368},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.23368},
}
RIS
TY - UNPB
TI - Broad Line Regions behind a Haze II: A Three-dimensional Electron-scattering Model of the Broad Brγ Line in NGC 3783
AU - Keiichi Wada
AU - Bert Vander Meulen
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2610.23368
UR - https://arxiv.org/abs/2610.23368
AB - We investigate the broad Brγ line in the type-1 active galactic nucleus NGC 3783 using three-dimensional Monte Carlo electron-scattering radiative transfer with SKIRT. Paper-I reproduced the observed smooth core and broad wings by convolving an intrinsic Keplerian profile with the analytic electron-scattering kernel of Laor (2006). Here we instead transport photons through explicit source and scattering geometries. For a partially covered Keplerian source, three-dimensional transfer broadens only the scattered photons and leaves an unscattered double-peaked core. For the thin Keplerian source motivated by Paper-I, a comparison of four scattering-geometry classes shows that neither a disk-like scatterer nor the tested halo variants reproduce both the core and wings. We therefore construct a two-component-source (2CS) model containing an inner Keplerian source disk, a rotating disk haze, a nearly spherical halo haze, and direct emission from a slower outer disk. A reference 2CS calculation gives Xi^2 =1.154 at i=15 deg. Polar cones with an input radial optical depth tau_hole=0.1 preserve the line profile and give a measured Thomson-thin sightline. The preferred low redistribution width, full-column ionization, and weak recombination emission cannot all be realized by a uniform thermal halo. The 2CS model is therefore a physically motivated parametric description whose medium must ultimately be tested with self-consistent radiative transfer, ionization, and dynamics.
ER -