No Luminous Little Red Dots: A Sharp Cutoff in Their Luminosity Function
10 affiliations
- 1Princeton University
- 2Sorbonne Université
- 3Centro de Astrobiología (CAB)
- 4University of Arizona
- 5The University of Texas at Austin
- 6Swinburne University of Technology
- 7Tsinghua University
- 8Tufts University
- 9Institute of Science and Technology Austria (ISTA)
- 10Saint Mary’s University
Abstract
One of the most surprising results of early James Webb Space Telescope (JWST) observations is the discovery of an abundance of red, compact, broad-line objects dubbed “little red dots” (LRDs) at z > 4. Their spatial density (∼10 −4 –10 −5 cMpc −3 ) is 100 times more abundant than UV-selected quasars at that redshift if one extrapolates the quasar luminosity function (QLF) down to the LRD regime. However, whether LRDs dominate black hole accretion at quasar-like luminosities ( L bol ≳ 10 45−46 erg s −1 ) remains unanswered, as probing the bright end of the LRD luminosity function requires a much larger area than that which is able to be surveyed by JWST. In this work, we present our search for the brightest LRDs ( K < 23.7) at 4.5 < z < 4.9 using wide-area multiwavelength imaging surveys from the near-UV to the infrared bands. With over 15 deg 2 of sky coverage, we only identify one single LRD candidate at z phot ≈ 4.6, which translates into a spatial density of n ( M 5100 < −23.5) ≈ 10 −8 cMpc −3 —this is nearly 10 times less abundant than the UV-selected quasars at similar optical luminosity. When combined with the LRD sample identified by JWST at the same redshift range, we find a sharp cutoff in the optical luminosity function at λL 5100 ≈ 2.2 × 10 44 erg s −1 , while the quasar luminosity function (QLF) turnover occurs at ≳20 times higher luminosity. We therefore confirm the exclusively low-luminosity nature of LRDs, ruling out that LRDs are the counterparts of quasars. Furthermore, we speculate that, if the shape of the luminosity function holds up, it points to LRDs being powered by low-mass black holes with a narrow range of Eddington-level accretion rates.
Related
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- Balmer Absorption Series and Broad Metal Lines in Two Luminous Little Red Dots
- A Little Red Dot emerging from a nitrogen-rich UV-luminous galaxy with Very Massive Stars
- Non-LTE radiative transfer models of very luminous sources and their applicability to little red dots, quasi-stars, and similar objects
- A Spectral Framework for Testing the Quasi-Star Hypothesis in Little Red Dots I: Weighing LRDs by Their Super-Eddington Luminosity Ratios---No Signs of Overmassive Black Holes
BibTeX
@article{ma2026luminous,
title = {{No Luminous Little Red Dots: A Sharp Cutoff in Their Luminosity Function}},
author = {Yilun Ma and Jenny E. Greene and Marta Volonteri and Andy D. Goulding and David J. Setton and Marianna Annunziatella and Eiichi Egami and Xiaohui Fan and Vasily Kokorev and Ivo Labbé and Xiaojing Lin and Danilo Marchesini and Jorryt Matthee and Themiya Nanayakkara and Lucy Robbins and Anna Sajina and Marcin Sawicki},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = sep,
doi = {10.3847/2041-8213/aea071},
url = {https://doi.org/10.3847/2041-8213/aea071},
note = {CC BY},
}
RIS
TY - JOUR
TI - No Luminous Little Red Dots: A Sharp Cutoff in Their Luminosity Function
AU - Yilun Ma
AU - Jenny E. Greene
AU - Marta Volonteri
AU - Andy D. Goulding
AU - David J. Setton
AU - Marianna Annunziatella
AU - Eiichi Egami
AU - Xiaohui Fan
AU - Vasily Kokorev
AU - Ivo Labbé
AU - Xiaojing Lin
AU - Danilo Marchesini
AU - Jorryt Matthee
AU - Themiya Nanayakkara
AU - Lucy Robbins
AU - Anna Sajina
AU - Marcin Sawicki
PY - 2026
DA - 2026/09/10
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/aea071
UR - https://doi.org/10.3847/2041-8213/aea071
AB - One of the most surprising results of early James Webb Space Telescope (JWST) observations is the discovery of an abundance of red, compact, broad-line objects dubbed “little red dots” (LRDs) at z > 4. Their spatial density (∼10 −4 –10 −5 cMpc −3 ) is 100 times more abundant than UV-selected quasars at that redshift if one extrapolates the quasar luminosity function (QLF) down to the LRD regime. However, whether LRDs dominate black hole accretion at quasar-like luminosities ( L bol ≳ 10 45−46 erg s −1 ) remains unanswered, as probing the bright end of the LRD luminosity function requires a much larger area than that which is able to be surveyed by JWST. In this work, we present our search for the brightest LRDs ( K < 23.7) at 4.5 < z < 4.9 using wide-area multiwavelength imaging surveys from the near-UV to the infrared bands. With over 15 deg 2 of sky coverage, we only identify one single LRD candidate at z phot ≈ 4.6, which translates into a spatial density of n ( M 5100 < −23.5) ≈ 10 −8 cMpc −3 —this is nearly 10 times less abundant than the UV-selected quasars at similar optical luminosity. When combined with the LRD sample identified by JWST at the same redshift range, we find a sharp cutoff in the optical luminosity function at λL 5100 ≈ 2.2 × 10 44 erg s −1 , while the quasar luminosity function (QLF) turnover occurs at ≳20 times higher luminosity. We therefore confirm the exclusively low-luminosity nature of LRDs, ruling out that LRDs are the counterparts of quasars. Furthermore, we speculate that, if the shape of the luminosity function holds up, it points to LRDs being powered by low-mass black holes with a narrow range of Eddington-level accretion rates.
SN - 2041-8205
SN - 2041-8213
ER -