Exploring the Nature of Little Red Dots: Constraints on Active Galactic Nucleus and Stellar Contributions from PRIMER MIRI Imaging

Abstract JWST has revealed a large population of compact, red objects at z > 4 known as Little Red Dots (LRDs). We analyze the spectral energy distributions (SEDs) of 88 LRDs from the JWST PRIMER survey with complete photometric coverage from 1 to 18 μ m using NIRCam and MIRI imaging, representing the most extensive SED analysis on a large LRD sample with long-wavelength MIRI data. We examine SED models in which either galaxy or active galactic nucleus (AGN) emission dominates the rest-frame UV or optical continuum, extracting physical properties to explore each scenario’s implications. In the galaxy-only model, we find massive, dusty stellar populations alongside unobscured, low-mass components, hinting at inhomogeneous obscuration. The AGN-only model indicates dusty, luminous AGNs with low hot dust fractions compared to typical quasars. A hybrid AGN and galaxy model suggests low-mass, unobscured galaxies in the UV, with stellar mass estimates spanning ∼2 dex across the different models, underscoring the need for caution in interpreting LRD stellar masses. With MIRI photometry, the galaxy-only model produces stellar masses within cosmological limits, but extremely high stellar mass densities are inferred. The hybrid model infers highly overmassive black holes exceeding those in recently reported high-redshift AGNs, hinting at a partial AGN contribution to the rest-optical continuum or widespread super-Eddington accretion. Our findings highlight the extreme conditions required for both AGN- and galaxy-dominated scenarios in LRDs, supporting a mixed contribution to the red continuum, or novel scenarios to explain the observed emission.

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Publication Details

Journal
The Astrophysical Journal
Published
2025-10-03
DOI
https://doi.org/10.3847/1538-4357/adfcce
Citations
17
Primary Topic
Astronomy and Astrophysical Research
Type
article
Field-Weighted Citation Impact
20.26
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article

Exploring the Nature of Little Red Dots: Constraints on Active Galactic Nucleus and Stellar Contributions from PRIMER MIRI Imaging

Ray A. Lucas, Adam C. Carnall, Alexa M. Morales, Hollis B. Akins et al.
17 citations
The Astrophysical Journal
Astronomy and Astrophysical Research
20.26
article

Exploring the Nature of Little Red Dots: Constraints on Active Galactic Nucleus and Stellar Contributions from PRIMER MIRI Imaging

Ray A. Lucas, Adam C. Carnall, Alexa M. Morales, Hollis B. Akins, Vasily Kokorev, Norman A. Grogin, Óscar A. Chávez Ortiz, Gene C. K. Leung, J. S. Dunlop, Callum T. Donnan, Casey Papovich, Anton M. Koekemoer, Anthony J. Taylor, Pablo G. Pérez‐González, D J McLeod, L. Y. Aaron Yung, Fergus Cullen, Guillermo Barro, Nikko J. Cleri, Steven L. Finkelstein, Dale D. Kocevski, Richard S. Ellis, Michaela Hirschmann
article en
17 citations

Abstract

Abstract JWST has revealed a large population of compact, red objects at z > 4 known as Little Red Dots (LRDs). We analyze the spectral energy distributions (SEDs) of 88 LRDs from the JWST PRIMER survey with complete photometric coverage from 1 to 18 μ m using NIRCam and MIRI imaging, representing the most extensive SED analysis on a large LRD sample with long-wavelength MIRI data. We examine SED models in which either galaxy or active galactic nucleus (AGN) emission dominates the rest-frame UV or optical continuum, extracting physical properties to explore each scenario’s implications. In the galaxy-only model, we find massive, dusty stellar populations alongside unobscured, low-mass components, hinting at inhomogeneous obscuration. The AGN-only model indicates dusty, luminous AGNs with low hot dust fractions compared to typical quasars. A hybrid AGN and galaxy model suggests low-mass, unobscured galaxies in the UV, with stellar mass estimates spanning ∼2 dex across the different models, underscoring the need for caution in interpreting LRD stellar masses. With MIRI photometry, the galaxy-only model produces stellar masses within cosmological limits, but extremely high stellar mass densities are inferred. The hybrid model infers highly overmassive black holes exceeding those in recently reported high-redshift AGNs, hinting at a partial AGN contribution to the rest-optical continuum or widespread super-Eddington accretion. Our findings highlight the extreme conditions required for both AGN- and galaxy-dominated scenarios in LRDs, supporting a mixed contribution to the red continuum, or novel scenarios to explain the observed emission.

The Astrophysical JournalVol. 992(1)
University of the Pacific (US), Space Telescope Science Institute (US), Pennsylvania State University (US), Colby College (US), Mitchell Institute (US), Kavli Institute for Particle Astrophysics and Cosmology (US), Royal Observatory (GB), Université Bourgogne Franche-Comté (FR), Centro de Astrobiología (ES), University College London (GB), École Polytechnique Fédérale de Lausanne (CH), The University of Texas at Austin (US), Texas A&M University (US), University of Edinburgh (GB)
Openalex Percentile: Top 0%
Astronomy and Astrophysical Research
20.26
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