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

2025/07/14 by Xiaojing Lin, Lin, Xiaojing, Xiaohui Fan +54 · 4 voices · 14 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph.CO #astro-ph.GA #astro-ph.SR

paper · pdf · doi:10.48550/arxiv.2507.10659

openalex publication_date 2025/07/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

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 z = 0.1-0.2, 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 Hα 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. The WISE-detected IR emission is consistent with weak dust emission of T ∼ 10²-10³ 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.

Citations

• Weakness of X-rays and variability in high-redshift active galactic nuclei with super-Eddington accretion
• The Chandra Source Catalog Release 2 Series
• ArXiv
• Overview of the DESI Legacy Imaging Surveys
• THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE): MISSION DESCRIPTION AND INITIAL ON-ORBIT PERFORMANCE
• Classification parameters for the emission-line spectra of extragalactic objects

Cited by

• Reduced Incidence of Little Red Dots at z < 3 from Number Density and Halo Mass Evolution
• Evolution of Size, Mass, and Density of Galaxies Since Cosmic Dawn
• Balmer Transition Signatures from Gas-Enshrouded, Dust-Poor Active Galactic Nuclei
• A Black-Hole Envelope Interpretation for Cosmological Demographics of Little Red Dots
• COSMOS-3D: Two obscured X-ray AGNs with hot dust and He Iλ10830 absorption at z~3
• Discovery of two little red dots transitioning into quasars
• Too Quiet for Comfort: Local Little Red Dots Lack Variability over Decades
• The Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot
• From nuclear star clusters to Little Red Dots: black hole growth, mergers, and tidal disruptions
• A z≃0.4 Little Red Dot analog: An Extended Starburst with an Overmassive Black hole
• The mechanism for creating "dynamical gravastar" black hole mimickers also explains formation of "little red dots"
• Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts
• Discovery of Multiply Ionized Iron Emission Powered by an Active Galactic Nucleus in a z~7 Little Red Dot
• MEGA: Spectrophotometric SED Fitting of Little Red Dots Detected in JWST MIRI

Discussions

• Whoa. Three Little Red Dots have now been found in SDSS! arxiv.org/abs/2507.10659 But due to their compact morphology and bizarre colors, they are originally selected as *quasar candidates*, not galax [bsky, 30 points, 0 comments]
• 12/12 Research paper: "The Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes"➡️ arxiv.org/abs/2507.10659 🔭 🧪 #science #cosmology [bsky, 7 points, 1 comments]
• The Discovery of Little Red Dots in the Local Universe - Signatures of Cool Gas Envelopes: arxiv.org/abs/2507.10659 -> A Black Hole Egg That Forgot to Hatch: aasnova.org/2026/01/13/a... [bsky, 0 points, 0 comments]
• Low redshift little red dots: arxiv.org/abs/2507.10659 [bsky, 0 points, 0 comments]

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