Super-Eddington Little Blue Dots May Reionize Helium Too Early
Abstract
The James Webb Space Telescope (JWST) has identified an abundant population of faint Active Galactic Nuclei (AGN) at z ≳ 4 which display broad emission lines, compact morphologies, and blue ultraviolet--optical continua. These ``Little Blue Dots' (LBDs) have been suggested to belong to the same family of objects as the more controversial ``Little Red Dots' (LRDs), with differences between the two largely owing to viewing angle effects. In this scenario, super-Eddington accretion resulting in high Extreme UV (EUV) and weak X-ray emission is invoked to explain the properties of both populations. We study the consequences of this super-Eddington scenario for the timing of Helium reionization. We find that observations which support an end to helium reionization no earlier than z ≈ 3 disfavor scenarios in which the majority of observed 3 ≲ z ≲ 7 LBDs are highly super-Eddington. For our fiducial super-Eddington accretion scenario, we find that the fraction of the LBD population in this state must be ≲ 10%, assuming LBDs make up 5% of the M m UV < −18 galaxy population and have average escape fractions of 15%, comparable to recent observations. Our constraint assumes that LBDs dominate the Helium reionization budget, and would be tighter if bright quasars also contributed significantly. For a majority of LBDs to be super-Eddington, they would need to have small escape fractions (≲ 1.5%) and/or be less abundant than observations suggest. Our conclusions are sensitive to the shape of the EUV spectra of super-Eddington black holes, motivating further study.
Related
- Little red dots as obscured little blue dots: A super-Eddington unification model
- 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
- Little Red Dots As Super-Eddington Fountain Flows
- Little Red Dots as Intermediate Mass, Super-Eddington Engines: Insights from Type IIn Supernovae and The 1837-1856 Great Eruption of η Carinae
- Episodic super-Eddington accretion as a clue to overmassive black holes in the early Universe
BibTeX
@misc{cain2026supereddington,
title = {{Super-Eddington Little Blue Dots May Reionize Helium Too Early}},
author = {Christopher Cain and Brent Smith and Gibson B. Bowling and Yongda Zhu and Lily Whitler and Rafael Ortiz III and Anson D'Aloisio and Rogier Windhorst},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.28745},
eprint = {2608.28745},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.28745},
}
RIS
TY - UNPB
TI - Super-Eddington Little Blue Dots May Reionize Helium Too Early
AU - Christopher Cain
AU - Brent Smith
AU - Gibson B. Bowling
AU - Yongda Zhu
AU - Lily Whitler
AU - Rafael Ortiz III
AU - Anson D'Aloisio
AU - Rogier Windhorst
PY - 2026
DA - 2026/08/28
PB - arXiv
DO - 10.48550/arxiv.2608.28745
UR - https://arxiv.org/abs/2608.28745
AB - The James Webb Space Telescope (JWST) has identified an abundant population of faint Active Galactic Nuclei (AGN) at z ≳ 4 which display broad emission lines, compact morphologies, and blue ultraviolet--optical continua. These ``Little Blue Dots' (LBDs) have been suggested to belong to the same family of objects as the more controversial ``Little Red Dots' (LRDs), with differences between the two largely owing to viewing angle effects. In this scenario, super-Eddington accretion resulting in high Extreme UV (EUV) and weak X-ray emission is invoked to explain the properties of both populations. We study the consequences of this super-Eddington scenario for the timing of Helium reionization. We find that observations which support an end to helium reionization no earlier than z ≈ 3 disfavor scenarios in which the majority of observed 3 ≲ z ≲ 7 LBDs are highly super-Eddington. For our fiducial super-Eddington accretion scenario, we find that the fraction of the LBD population in this state must be ≲ 10%, assuming LBDs make up 5% of the M_ m UV < −18 galaxy population and have average escape fractions of 15%, comparable to recent observations. Our constraint assumes that LBDs dominate the Helium reionization budget, and would be tighter if bright quasars also contributed significantly. For a majority of LBDs to be super-Eddington, they would need to have small escape fractions (≲ 1.5%) and/or be less abundant than observations suggest. Our conclusions are sensitive to the shape of the EUV spectra of super-Eddington black holes, motivating further study.
ER -