The Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes

Abstract

JWST observations have revealed a population of high-redshift “little red dots” (LRDs) that challenge conventional active galactic nucleus (AGN) models. We report the discovery of three local LRDs at z = 0.1–0.2, initially selected from the Sloan Digital Sky Survey 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 spectral energy distribution, 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 α 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 “The Egg”), 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 (BHs). The Wide-field Infrared Survey Explorer–detected IR emission is consistent with weak dust emission of T  ∼ 10 2 –10 3 K. We propose a conceptual model consisting of a largely thermalized cool-gas envelope surrounding the central BH and an extended emission-line region with high-density outflowing gas to explain the observed properties of these local LRDs.