May
2026
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2026ApJ..1002....9L
Authors
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Li, Zi-Jian
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Zou, Siwei
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Lyu, Jianwei
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Champagne, Jaclyn B.
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Huang, Jia-Sheng
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Cheng, Cheng
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Fu, Shuqi
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Zhang, Zijian
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Jiang, Danyang
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Lee, Khee-Gan
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Wang, Feige
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Fan, Xiaohui
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Yang, Jinyi
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Li, Ruancun
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Akins, Hollis B.
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Bian, Fuyan
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Dai, Y. Sophia
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Faisst, Andreas L.
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Ho, Luis C.
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Inayoshi, Kohei
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Jiang, Linhua
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Jin, Xiangyu
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Kakiichi, Koki
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Kartaltepe, Jeyhan S.
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Li, Zihao
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Liu, Weizhe
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Schindler, Jan-Torge
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Tee, Wei Leong
Abstract
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We report the discovery of two broad-line X-ray active galactic nuclei (AGNs) (cid_414 and cid_947) at z ∼ 3 identified in the JWST Cycle 3 COSMOS-3D program using NIRCam F444W grism spectroscopy. Both exhibit prominent He Iλ10830 +Paγ emission and absorption, indicative of circumnuclear dense gas that is traced in these systems. Complementary UV and optical spectroscopy in the COSMOS field provides Lyα, Si IV, and C IV measurements. Both sources are detected in MIRI F1000W, and cid_414 is also detected in F2100W, indicating hot dust emission. The two AGNs show distinct black hole and obscuration properties. The source cid_414 displays little red dot (LRD)-like, V-shaped spectral energy distribution with a turnover near the Balmer 4000 Å break and a narrow Lyα line with logLLyα=42.49±0.01ergs−1 , with no additional metal lines detected. In contrast, cid_947 exhibits a higher He Iλ10830 absorption column density, larger X-ray─inferred NH, lower intrinsic 2─10 keV luminosity, and strong blueshifted features in He I, Si IV, and C IV absorption with velocity offsets exceeding 5000 km s−1. Photoionization modeling implies gas densities of ∼109−10 cm−3 and sizes comparable to the broad-line region, consistent with dense gas envelopes predicted for LRDs. Together with previous detections of He Iλ10830 absorption in compact LRDs, these results suggest that dense circumnuclear gas is likely prevalent at high redshift and may regulate obscuration and black hole─host coevolution across AGN types.
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