Little red dots as obscured little blue dots: A super-Eddington unification model
Year: 2026
Type: article
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.
Source: Astronomy and Astrophysics
Authors: Piero Madau, Roberto Maiolino
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7131881103