UNCOVER: 404 Error—Models Not Found for the Triply Imaged Little Red Dot A2744-QSO1*

Abstract JWST has revealed an abundance of compact, red objects at z ≈ 5–8 dubbed “little red dots” (LRDs), whose SEDs display a faint blue UV continuum followed by a steep rise in the optical. Despite extensive study of their characteristic V-shaped SEDs, the nature of LRDs remains unknown. We present a new analysis of the NIRSpec/PRISM spectrum of A2744-QSO1, a triply imaged LRD at z = 7.04 from the UNCOVER survey. The spectrum shows a strong Balmer break and broad Balmer emission lines, both of which are difficult to explain with models invoking exclusively AGN or stellar contributions. Our fiducial model decomposes the spectrum into a post-starburst galaxy dominating the UV-optical continuum and a reddened AGN being subdominant at all wavelengths and contributing at a level of ∼20%. However, this model infers a stellar mass of M ⋆ ≈ 4 × 10 9 M ⊙ within a radius of r e < 30 pc, driving its central density to the highest among observations to date. This high central density could be explained if A2744-QSO1 is the early-forming core of a modern-day massive elliptical galaxy that later puffed up via the inside-out growth channel. The models also necessitate an unusually steep dust extinction law to preserve the strong break strength, though this steepness may be explained by a deficit of large dust grains. It is also probable that these challenges reflect our ignorance of A2744-QSO1's true nature. Future variability and reverberation mapping studies could help disentangle the galaxy and AGN contribution to the continuum, and deeper redder observations could also unveil the dust properties in LRDs.

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Publication Details

Journal
The Astrophysical Journal
Published
2025-03-07
DOI
https://doi.org/10.3847/1538-4357/ada613
Citations
37
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
42.73

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article

UNCOVER: 404 Error—Models Not Found for the Triply Imaged Little Red Dot A2744-QSO1*

Pratika Dayal, Lukas J. Furtak, Rachel Bezanson, Vasily Kokorev et al.
37 citations
The Astrophysical Journal
Galaxies: Formation, Evolution, Phenomena
42.73
article

UNCOVER: 404 Error—Models Not Found for the Triply Imaged Little Red Dot A2744-QSO1*

Pratika Dayal, Lukas J. Furtak, Rachel Bezanson, Vasily Kokorev, Karl Glazebrook, Sam E. Cutler, Richard Pan, Jenny E. Greene, Ivo Labbé, John R. Weaver, David J. Setton, Christina C. Williams, Andy D. Goulding, Joel Leja, Pieter van Dokkum, Gabriel Brammer, Katherine E. Whitaker, Adi Zitrin, Sedona H. Price, Yilun Ma, Marta Volonteri, Anna de Graaff, Bingjie Wang
article en
37 citations

Abstract

Abstract JWST has revealed an abundance of compact, red objects at z ≈ 5–8 dubbed “little red dots” (LRDs), whose SEDs display a faint blue UV continuum followed by a steep rise in the optical. Despite extensive study of their characteristic V-shaped SEDs, the nature of LRDs remains unknown. We present a new analysis of the NIRSpec/PRISM spectrum of A2744-QSO1, a triply imaged LRD at z = 7.04 from the UNCOVER survey. The spectrum shows a strong Balmer break and broad Balmer emission lines, both of which are difficult to explain with models invoking exclusively AGN or stellar contributions. Our fiducial model decomposes the spectrum into a post-starburst galaxy dominating the UV-optical continuum and a reddened AGN being subdominant at all wavelengths and contributing at a level of ∼20%. However, this model infers a stellar mass of M ⋆ ≈ 4 × 10 9 M ⊙ within a radius of r e < 30 pc, driving its central density to the highest among observations to date. This high central density could be explained if A2744-QSO1 is the early-forming core of a modern-day massive elliptical galaxy that later puffed up via the inside-out growth channel. The models also necessitate an unusually steep dust extinction law to preserve the strong break strength, though this steepness may be explained by a deficit of large dust grains. It is also probable that these challenges reflect our ignorance of A2744-QSO1's true nature. Future variability and reverberation mapping studies could help disentangle the galaxy and AGN contribution to the continuum, and deeper redder observations could also unveil the dust properties in LRDs.

The Astrophysical JournalVol. 981(2)
Institut d'Astrophysique de Paris (FR), Damien Foundation (BD)
National Science Foundation, National Aeronautics and Space Administration, Space Telescope Science Institute, European Commission, Rijksuniversiteit Groningen, United States-Israel Binational Science Foundation, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Israel Science Foundation
Openalex Percentile: Top 0%
Galaxies: Formation, Evolution, Phenomena
42.73
DOIOpen Access PDFOpenAlex
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