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

Authors

• Gene C.K. Leung, The University of Texas at Austin
• Steven L. Finkelstein, The University of Texas at Austin
• Pablo G. Pérez-González, CSIC-INTA - Centro de Astrobiología (CAB)
• Alexa M. Morales, The University of Texas at Austin
• Anthony J. Taylor, The University of Texas at Austin
• Guillermo Barro, University of the PacificFollow
• Dale D. Kocevski, Colby College
• Hollis B. Akins, The University of Texas at Austin
• Adam C. Carnall, University of Edinburgh, Institute for Astronomy
• Óscar A. Chávez Ortiz, The University of Texas at Austin
• Nikko J. Cleri, Pennsylvania State University
• Fergus Cullen, University of Edinburgh, Institute for Astronomy
• Callum T. Donnan, University of Edinburgh, Institute for Astronomy
• James S. Dunlop, University of Edinburgh, Institute for Astronomy
• Richard S. Ellis, University College London
• Norman A. Grogin, Space Telescope Science Institute
• Michaela Hirschmann, École Polytechnique Fédérale de Lausanne
• Anton M. Koekemoer, Space Telescope Science Institute
• Vasily Kokorev, The University of Texas at Austin
• Ray A. Lucas, Space Telescope Science Institute
• Derek J. McLeod, University of Edinburgh, Institute for Astronomy

Document Type

Article

Publication Title

Astrophysical Journal

Department

Physics

ISSN

15384357

Volume

992

Issue

1

DOI

10.3847/1538-4357/adfcce

First Page

1

Last Page

19

Publication Date

10-3-2025

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 μm 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.

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Recommended Citation

Leung, Gene C.K.; Finkelstein, Steven L.; Pérez-González, Pablo G.; Morales, Alexa M.; Taylor, Anthony J.; Barro, Guillermo; Kocevski, Dale D.; Akins, Hollis B.; Carnall, Adam C.; Chávez Ortiz, Óscar A.; Cleri, Nikko J.; Cullen, Fergus; Donnan, Callum T.; Dunlop, James S.; Ellis, Richard S.; Grogin, Norman A.; Hirschmann, Michaela; Koekemoer, Anton M.; Kokorev, Vasily; Lucas, Ray A.; and McLeod, Derek J., "Exploring the Nature of Little Red Dots: Constraints on Active Galactic Nucleus and Stellar Contributions from PRIMER MIRI Imaging" (2025). Pacific Faculty Work. 94.
https://scholarlycommons.pacific.edu/all-faculty/94