Little red dots as obscured little blue dots: A super-Eddington unification model
5 affiliations
- 1Department of Astronomy & Astrophysics, University of California
- 2Dipartimento di Fisica “G. Occhialini,” Università degli Studi di Milano-Bicocca
- 3Cavendish Laboratory, University of Cambridge
- 4Department of Physics and Astronomy, University College London
- 5Kavli Institute for Cosmology, University of Cambridge
Abstract
We investigated whether little red dots (LRDs) are the dust-reddened, high-inclination counterparts of compact, blue broad-line AGNs (“little blue dots”; LBDs) powered by super-Eddington accretion. We modeled the central engine as a geometrically thick, radiation-pressure supported accretion flow whose funnel produces strongly anisotropic, intrinsically blue ionizing continua. This is coupled to an equatorially concentrated broad-line region (BLR) and dusty reprocessing clouds with a modest covering factor. Using inclination-dependent spectral energy distributions (SEDs) as input to CLOUDY, we show that the extreme broad H α equivalent widths (EWs) of JWST LRDs can be reproduced with global BLR covering factors of only C BLR ≃ 0.1, fully consistent with standard type 1 active galactic nuclei (AGNs) and far below unity. Large Balmer EWs arise because self-shadowing suppresses the high-inclination optical continuum while the BLR is illuminated by an ionizing-rich extreme ultraviolet (EUV) SED. Weak high-ionization lines (e.g., He II λ 4686) follow from the orientation-dependent suppression of the hard extreme ultraviolet (XUV) and soft X-ray continuum toward equatorial directions, without requiring a fully enclosing gaseous “cocoon.” Applying a gray dust attenuation law with A V ≃ 3 along high-inclination (LRD-selected) sightlines, our fiducial model reproduces the V-shaped UV–optical continua of LRDs and the large Balmer decrements. Strong Balmer breaks arise only along the most obscured sightlines. A compact equatorial dust structure with a modest global covering factor intercepts and reradiates only a small fraction of the bolometric luminosity, yielding a modest hot-dust bump and far-infrared and submillimeter output consistent with current measurements and limits and implying small dust masses. This single-framework model links LRD and LBD observables through orientation, predicting correlated trends in H α EW, Balmer decrement, Balmer break, high-ionization line strengths, and infrared emission.
Related
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- Little red dots as obscured little blue dots: Relative abundances, luminosities, and black hole masses
BibTeX
@article{madau2026little,
title = {{Little red dots as obscured little blue dots: A super-Eddington unification model}},
author = {Piero Madau and R. Maiolino},
journal = {Astronomy and Astrophysics},
year = {2026},
month = sep,
doi = {10.1051/0004-6361/202659606},
url = {https://doi.org/10.1051/0004-6361/202659606},
note = {CC BY},
}
RIS
TY - JOUR
TI - Little red dots as obscured little blue dots: A super-Eddington unification model
AU - Piero Madau
AU - R. Maiolino
PY - 2026
DA - 2026/09/03
JO - Astronomy and Astrophysics
DO - 10.1051/0004-6361/202659606
UR - https://doi.org/10.1051/0004-6361/202659606
AB - We investigated whether little red dots (LRDs) are the dust-reddened, high-inclination counterparts of compact, blue broad-line AGNs (“little blue dots”; LBDs) powered by super-Eddington accretion. We modeled the central engine as a geometrically thick, radiation-pressure supported accretion flow whose funnel produces strongly anisotropic, intrinsically blue ionizing continua. This is coupled to an equatorially concentrated broad-line region (BLR) and dusty reprocessing clouds with a modest covering factor. Using inclination-dependent spectral energy distributions (SEDs) as input to CLOUDY, we show that the extreme broad H α equivalent widths (EWs) of JWST LRDs can be reproduced with global BLR covering factors of only C BLR ≃ 0.1, fully consistent with standard type 1 active galactic nuclei (AGNs) and far below unity. Large Balmer EWs arise because self-shadowing suppresses the high-inclination optical continuum while the BLR is illuminated by an ionizing-rich extreme ultraviolet (EUV) SED. Weak high-ionization lines (e.g., He II λ 4686) follow from the orientation-dependent suppression of the hard extreme ultraviolet (XUV) and soft X-ray continuum toward equatorial directions, without requiring a fully enclosing gaseous “cocoon.” Applying a gray dust attenuation law with A V ≃ 3 along high-inclination (LRD-selected) sightlines, our fiducial model reproduces the V-shaped UV–optical continua of LRDs and the large Balmer decrements. Strong Balmer breaks arise only along the most obscured sightlines. A compact equatorial dust structure with a modest global covering factor intercepts and reradiates only a small fraction of the bolometric luminosity, yielding a modest hot-dust bump and far-infrared and submillimeter output consistent with current measurements and limits and implying small dust masses. This single-framework model links LRD and LBD observables through orientation, predicting correlated trends in H α EW, Balmer decrement, Balmer break, high-ionization line strengths, and infrared emission.
SN - 0004-6361
SN - 1432-0746
ER -