Paper
The Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes
Authors
Xiaojing Lin, Xiaohui Fan, Zheng Cai, Fuyan Bian, Hanpu Liu, Fengwu Sun, Yilun Ma, Jenny E. Greene, Michael A. Strauss, Richard Green, Jianwei Lyu, Jaclyn B. Champagne, Andy D. Goulding, Kohei Inayoshi, Xiangyu Jin, Gene C. K. Leung, Mingyu Li, Weizhe Liu, Yichen Liu, Junjie Mao, Maria Anne Pudoka, Wei Leong Tee, Ben Wang, Feige Wang, Yunjing Wu, Jinyi Yang, Haowen Zhang, Yongda Zhu
Abstract
JWST observations have revealed a population of high-redshift "little red dots" (LRDs) that challenge conventional AGN models. We report the discovery of three local LRDs at -, initially selected from the SDSS database, with follow-up optical/near-IR spectroscopy and photometry. They exhibit properties fully consistent with those of high-redshift LRDs, including broad hydrogen and helium emission lines, compact morphologies, V-shaped UV-optical SED, declining near-IR continua, and no significant variability. Two sources were targeted but not detected in X-rays with statistical significance. All three sources show blue-shifted He I absorption, while two exhibit H and Na D absorption lines. We detect full Balmer and Paschen line series in all three objects, along with abundant narrow [Fe II] emission in two. The emission line analyses suggest narrow lines originate from AGN-powered, metal-poor regions with minimal dust; broad lines come from inner regions with exceptionally high density or atypical dust properties; and [Fe II] emission arises from dense gas between broad and narrow-line regions. One of our objects, J1025+1402 (nicknamed ), shows extremely high equivalent width Na D, K I, and Ca II triplet absorption lines, along with other potential low-ionization absorption features, suggesting the presence of a cool (5000 K), metal-enriched gas envelope. The optical/near-IR continua of these LRDs are also consistent with theoretical models featuring an atmosphere around black holes. The WISE-detected IR emission is consistent with weak dust emission of K. We propose a conceptual model consisting of a largely thermalized cool-gas envelope surrounding the central black hole and an extended emission line region with high-density outflowing gas to explain the observed properties of these local LRDs.