Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime
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...
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2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ada386 |
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| author | Qiaoya Wu Yue Shen Hengxiao Guo Scott F. Anderson W. N. Brandt Catherine J. Grier Patrick B. Hall Luis C. Ho Yasaman Homayouni Keith Horne Jennifer I-Hsiu Li Donald P. Schneider |
| author_facet | Qiaoya Wu Yue Shen Hengxiao Guo Scott F. Anderson W. N. Brandt Catherine J. Grier Patrick B. Hall Luis C. Ho Yasaman Homayouni Keith Horne Jennifer I-Hsiu Li Donald P. Schneider |
| author_sort | Qiaoya Wu |
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| description | 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 ( $\mathrm{log}\,{U}_{{\rm{H}}}=-2$ ) and hydrogen density ( $\mathrm{log}\,n({\rm{H}})=12$ ) can qualitatively reproduce the observed global R – L relation for the current RM AGN sample. However, such models fail to reproduce the observed decrease in BLR size with increasing L / L _Edd at fixed optical luminosity, implying that gas density or BLR structure may systematically change with accretion rate. |
| format | Article |
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| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-e3d8e9f3b24b4d8bb43e99d5575087c62025-02-08T05:49:39ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01980113410.3847/1538-4357/ada386Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion RegimeQiaoya Wu0https://orcid.org/0000-0003-4202-1232Yue Shen1https://orcid.org/0000-0003-1659-7035Hengxiao Guo2https://orcid.org/0000-0001-8416-7059Scott F. Anderson3https://orcid.org/0000-0002-6404-9562W. N. Brandt4https://orcid.org/0000-0002-0167-2453Catherine J. Grier5https://orcid.org/0000-0001-9920-6057Patrick B. Hall6https://orcid.org/0000-0002-1763-5825Luis C. Ho7https://orcid.org/0000-0001-6947-5846Yasaman Homayouni8https://orcid.org/0000-0002-0957-7151Keith Horne9https://orcid.org/0000-0003-1728-0304Jennifer I-Hsiu Li10https://orcid.org/0000-0002-0311-2812Donald P. Schneider11https://orcid.org/0000-0001-7240-7449Department of Astronomy, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USA ; [email protected], [email protected] of Astronomy, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USA ; [email protected], [email protected]; National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USAShanghai Astronomical Observatory , Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, People’s Republic of ChinaAstronomy Department, University of Washington , Box 351580, Seattle, WA 98195, USADepartment of Astronomy and Astrophysics, The Pennsylvania State University , University Park, PA 16802, USA; Institute for Gravitation and the Cosmos, The Pennsylvania State University , University Park, PA 16802, USA; Department of Physics, 104 Davey Laboratory, The Pennsylvania State University , University Park, PA 16802, USADepartment of Astronomy, University of Wisconsin–Madison , Madison, WI 53706, USADepartment of Physics and Astronomy, York University , 4700 Keele Street, Toronto, ON M3J 1P3, CanadaKavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871, People’s Republic of China; Department of Astronomy, School of Physics, Peking University , Beijing 100871, People’s Republic of ChinaDepartment of Astronomy and Astrophysics, The Pennsylvania State University , University Park, PA 16802, USA; Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USASUPA Physics and Astronomy, University of St Andrews , Fife, KY16 9SS, UKMichigan Institute for Data Science, University of Michigan , Ann Arbor, MI 48109, USA; Department of Astronomy, University of Michigan , Ann Arbor, MI 48109, USADepartment of Astronomy and Astrophysics, The Pennsylvania State University , University Park, PA 16802, USA; Institute for Gravitation and the Cosmos, The Pennsylvania State University , University Park, PA 16802, USAOver 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 ( $\mathrm{log}\,{U}_{{\rm{H}}}=-2$ ) and hydrogen density ( $\mathrm{log}\,n({\rm{H}})=12$ ) can qualitatively reproduce the observed global R – L relation for the current RM AGN sample. However, such models fail to reproduce the observed decrease in BLR size with increasing L / L _Edd at fixed optical luminosity, implying that gas density or BLR structure may systematically change with accretion rate.https://doi.org/10.3847/1538-4357/ada386Black hole physicsQuasarsActive galactic nuclei |
| spellingShingle | Qiaoya Wu Yue Shen Hengxiao Guo Scott F. Anderson W. N. Brandt Catherine J. Grier Patrick B. Hall Luis C. Ho Yasaman Homayouni Keith Horne Jennifer I-Hsiu Li Donald P. Schneider Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime The Astrophysical Journal Black hole physics Quasars Active galactic nuclei |
| title | Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime |
| title_full | Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime |
| title_fullStr | Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime |
| title_full_unstemmed | Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime |
| title_short | Understanding the Broad-line Region of Active Galactic Nuclei with Photoionization. I. The Moderate-accretion Regime |
| title_sort | understanding the broad line region of active galactic nuclei with photoionization i the moderate accretion regime |
| topic | Black hole physics Quasars Active galactic nuclei |
| url | https://doi.org/10.3847/1538-4357/ada386 |
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