Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime

作者：Qiaoya Wu, Yue Shen, Hengxiao Guo, Scott F. Anderson, W. N. Brandt, C. J. Grier, Patrick B. Hall, Luis C. Ho, Y. Homayouni, K. Horne, Jennifer I-Hsiu Li, Donald P. Schneider · 发表于：The Astrophysical Journal · 年份：2025 · DOI：10.3847/1538-4357/ada386 · 被引用次数：5 · 研究领域：Astrophysical Phenomena and Observations、Galaxies: Formation, Evolution, Phenomena、Astrophysics and Star Formation Studies

Abstract Over three decades of reverberation mapping (RM) studies on local broad-line active galactic nuclei (AGNs) have measured reliable black hole (BH) masses for >100 AGNs. These RM measurements reveal a significant correlation between the Balmer broad-line region (BLR) size and AGN optical luminosity (the R – L relation). Recent RM studies for AGN samples with more diverse BH parameters (e.g., mass and Eddington ratio) reveal a substantial intrinsic dispersion around the average R – L relation, suggesting that variations in the broadband spectrum, driven by accretion parameters and other factors such as the cloud distribution and inclination, significantly influence the measured R – L relation. Here we perform a detailed photoionization investigation of expected broad-line properties as functions of accretion parameters using AGN continuum models from qsosed . We compare theoretical predictions with observations of a sample of 67 z ≲ 0.5 reverberation-mapped AGNs with rest-frame optical and UV spectra in the moderate-accretion regime (Eddington ratio λ Edd ≡ L / L Edd < 0.5). The UV/optical line strengths and their dependences on accretion parameters are reasonably well reproduced by the locally optimally emitting cloud photoionization models. We provide quantitative recipes using optical/UV line flux ratios to infer the unobservable ionizing continuum. Additionally, photoionization models with universal values of ionization parameter ( log U H ...