A Decade-scale Ionization Echo of Black Hole Accretion in Galactic Nuclei
11 affiliations
- 1Chinese Academy of Sciences
- 2Durham University
- 3Nanjing University
- 4University of Michigan
- 5European Southern Observatory
- 6International Gemini Observatory/NSF NOIRLab
- 7Peking University
- 8Nanjing Normal University
- 9Università di Firenze
- 10INAF–Osservatorio Astrofisico di Arcetri
- 11University of Chinese Academy of Sciences
Abstract
Circumnuclear structures in active galactic nuclei (AGN) respond to accretion variability over different spatial and temporal scales, but whether compact narrow-line gas responds on decade timescales has not been systematically established. We use repeat Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument spectroscopy of 473 variability-selected galactic nuclei with evidence for recent nuclear brightening. We identify 19 sources whose narrow [O III ] λ 5007 flux increased by more than a factor of 2 over rest-frame baselines of 12.0–20.4 yr, which we term narrow-line ionization echoes (NIEs). In equal-weight stacked spectra, [O III ] increased by 229% ± 22%, while lower-ionization lines remained nearly unchanged or declined, indicating an ionization-dependent response rather than uniform spectral rescaling. The NIE hosts also moved coherently toward higher excitation in optical diagnostic diagrams, with mean increases of 0.46 ± 0.18 dex in log ( [ O III ] / H β ) and 0.58 ± 0.13 dex in log ( [ O III ] / [ O II ] ) . Photoionization models reproduce this evolution with a higher ionization parameter and a harder AGN-like ionizing spectrum at fixed gas abundance. For 13 sources with well-defined mid-infrared (MIR) outbursts, the integrated W1+W2 excess energy correlates strongly with the absolute [O III ] luminosity change ( r = 0.87), linking the dust and narrow-line responses to the same nuclear event. The MIR timescale and spectroscopic baseline constrain the variable [O III ]-emitting gas to characteristic scales of 1.5–5.2 pc. Compact narrow-line gas therefore appears to form an intermediate, decade-scale response layer between the infrared dust echo and the long-lived extended narrow-line region.
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BibTeX
@article{guo2026decadescale,
title = {{A Decade-scale Ionization Echo of Black Hole Accretion in Galactic Nuclei}},
author = {Wei-Jian Guo and Shuo Zhai and Chen Hu and David M. Alexander and Bin Luo and Pu Du and Matthew J. Temple and Leah K. Morabito and Feige Wang and Jinyi Yang and Victoria A. Fawcett and Swayamtrupta Panda and Claire L. Greenwell and Yan-Rong Li and Cheng Cheng and Shengxiu Sun and Zhi-Qiang Chen and Alessandro Marconi and Jian-Min Wang},
journal = {The Astrophysical Journal},
year = {2026},
month = nov,
doi = {10.3847/1538-4357/aeae2b},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aeae2b},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - A Decade-scale Ionization Echo of Black Hole Accretion in Galactic Nuclei
AU - Wei-Jian Guo
AU - Shuo Zhai
AU - Chen Hu
AU - David M. Alexander
AU - Bin Luo
AU - Pu Du
AU - Matthew J. Temple
AU - Leah K. Morabito
AU - Feige Wang
AU - Jinyi Yang
AU - Victoria A. Fawcett
AU - Swayamtrupta Panda
AU - Claire L. Greenwell
AU - Yan-Rong Li
AU - Cheng Cheng
AU - Shengxiu Sun
AU - Zhi-Qiang Chen
AU - Alessandro Marconi
AU - Jian-Min Wang
PY - 2026
DA - 2026/11/04
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aeae2b
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aeae2b
AB - Circumnuclear structures in active galactic nuclei (AGN) respond to accretion variability over different spatial and temporal scales, but whether compact narrow-line gas responds on decade timescales has not been systematically established. We use repeat Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument spectroscopy of 473 variability-selected galactic nuclei with evidence for recent nuclear brightening. We identify 19 sources whose narrow [O III ] λ 5007 flux increased by more than a factor of 2 over rest-frame baselines of 12.0–20.4 yr, which we term narrow-line ionization echoes (NIEs). In equal-weight stacked spectra, [O III ] increased by 229% ± 22%, while lower-ionization lines remained nearly unchanged or declined, indicating an ionization-dependent response rather than uniform spectral rescaling. The NIE hosts also moved coherently toward higher excitation in optical diagnostic diagrams, with mean increases of 0.46 ± 0.18 dex in log ( [ O III ] / H β ) and 0.58 ± 0.13 dex in log ( [ O III ] / [ O II ] ) . Photoionization models reproduce this evolution with a higher ionization parameter and a harder AGN-like ionizing spectrum at fixed gas abundance. For 13 sources with well-defined mid-infrared (MIR) outbursts, the integrated W1+W2 excess energy correlates strongly with the absolute [O III ] luminosity change ( r = 0.87), linking the dust and narrow-line responses to the same nuclear event. The MIR timescale and spectroscopic baseline constrain the variable [O III ]-emitting gas to characteristic scales of 1.5–5.2 pc. Compact narrow-line gas therefore appears to form an intermediate, decade-scale response layer between the infrared dust echo and the long-lived extended narrow-line region.
SN - 1538-4357
SN - 0004-637X
ER -