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arXiv · 2511.15359

Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. V. Dramatic Variability in High-Ionization Broad Emission Lines

Zhi-Qiang Chen·Jun-Jie Jin·Wei-Jian Guo·Sheng-Xiu Sun·Zhi-Wei Pan·Chen-Xu Liu·Hua-Qing Cheng·Jing-Wei Hu·Zhen-Feng Sheng·Hu Zou·Zhao-Bin Chen·Qi Zheng·Qi-Rong Yuan
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Abstract

We present a systematic search for changing-look (CL) quasars at high redshift z > 0.9 by cross-matching the spectroscopic datasets from the Dark Energy Spectroscopic Instrument Data Release 1 and Sloan Digital Sky Survey Data Release 18. We identify 97 CL quasars showing significant variability in high-ionization broad emission lines, including 45 turn-on and 52 turn-off events, corresponding to a detection rate of approximately 0.042%. This rate is lower than that found for low-ionization CL quasars, likely due to both selection effects and physical differences in high-ionization lines. Based on the CL quasar sample, we find that CL quasars generally exhibit lower accretion rates compared to typical quasars, with average Eddington ratios of log lambda_Edd approximately -1.14 in the bright state and approximately -1.39 in the dim state, compared to approximately -0.65 for typical quasars. While high-ionization lines in CL quasars follow the Baldwin effect on a population level, some individual sources show inverse Baldwin trends. We also find a positive correlation between the variability of high-ionization lines such as Mg II and C III] and the change in bolometric luminosity. In addition, we estimate a characteristic rest-frame timescale of approximately 3 years for CL transitions, with no significant difference between turn-on and turn-off cases. Taken together, these results support an accretion-driven origin for the CL phenomenon and provide new insights into the variability of high-ionization emission lines.

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Zhi-Qiang Chen, Jun-Jie Jin, Wei-Jian Guo, Sheng-Xiu Sun, Zhi-Wei Pan, Chen-Xu Liu, Hua-Qing Cheng, Jing-Wei Hu, Zhen-Feng Sheng, Hu Zou, Zhao-Bin Chen, Qi Zheng, Qi-Rong Yuan. 2025-11-19. Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. V. Dramatic Variability in High-Ionization Broad Emission Lines. https://arxiv.org/abs/2511.15359

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