Velocity-resolved Ionization Mapping of the Broad-line Region. II. Signatures of Eccentric Broad-line Regions from a Quantitative Photoionization-Based Model

@misc{wu2026velocityresolved,
  title = {{Velocity-resolved Ionization Mapping of the Broad-line Region. II. Signatures of Eccentric Broad-line Regions from a Quantitative Photoionization-Based Model}},
  author = {Jiancheng Wu and Hai-Cheng Feng and Sha-Sha Li and Qingwen Wu and Xinwu Cao},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.25718},
  eprint = {2610.25718},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.25718},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Velocity-resolved Ionization Mapping of the Broad-line Region. II. Signatures of Eccentric Broad-line Regions from a Quantitative Photoionization-Based Model
AU  - Jiancheng Wu
AU  - Hai-Cheng Feng
AU  - Sha-Sha Li
AU  - Qingwen Wu
AU  - Xinwu Cao
PY  - 2026
DA  - 2026/10/19
PB  - arXiv
DO  - 10.48550/arxiv.2610.25718
UR  - https://arxiv.org/abs/2610.25718
AB  - Velocity-resolved reverberation mapping (RM) is one of the most powerful tools for probing the geometry and kinematics of the broad-line region in active galactic nuclei. However, its interpretation may be non-unique, as similar velocity-delay signatures can arise from different combinations of BLR geometry and kinematics. To address this degeneracy, this series of studies develops velocity-resolved ionization mapping (IM) as a complementary technique. In this second paper of the series, we construct photoionization-based BLR models to quantitatively demonstrate the diagnostic power of the joint RM+IM framework. We calculate local \ha\ and \hb\ emissivities with Cloudy, couple them with disk-like BLR models, and generate synthetic velocity-dependent line fluxes, lags, and Balmer decrements. The model reproduces the observed anti-correlation between the integrated BD and the incident ionizing continuum, with scatter naturally introduced by reverberation delays. We show that a virialized elliptical BLR can produce diverse velocity-delay maps and velocity-resolved lags that mimic RM signatures commonly attributed to virialized motion, inflow, or outflow. In contrast, the velocity-resolved BD is sensitive to the symmetry of the BLR gas distribution, providing a key diagnostic for distinguishing eccentric geometry from non-virial motions. Through proof-of-concept comparisons with one double-peaked and one single-peaked AGN, we show that an elliptical-disk BLR can simultaneously reproduce the observed line profiles, velocity-resolved lags, and velocity-resolved BDs. These results provide a quantitative basis for IM, support the presence of eccentric BLR structures in AGNs, and demonstrate the potential of joint RM+IM analyses to break the BLR geometry-kinematics degeneracy.
ER  -