Little Red Dots as Obscured Little Blue Dots: A Super-Eddington Unification Model

TL;DR

This paper proposes a unification model for 'Little Red Dots' and 'Little Blue Dots' AGNs, explaining their observed differences through orientation effects and detailed accretion flow modeling, consistent with JWST observations.

Contribution

It introduces a super-Eddington accretion model with anisotropic emission and orientation-dependent obscuration to unify the properties of LRDs and LBDs, supported by detailed spectral simulations.

Findings

Reproduces extreme broad Halpha EWs with low BLR covering factors.

Explains weak high-ionization lines via orientation-dependent continuum suppression.

Matches UV-optical continua and IR emission with modest dust components.

Abstract

We test whether "Little Red Dots" (LRDs) are dust-reddened, high-inclination counterparts of compact, blue broad-line AGNs ("Little Blue Dots", LBDs) powered by super-Eddington accretion. We model the central engine as a geometrically thick, radiation-pressure supported accretion flow whose funnel yields strongly anisotropic, intrinsically blue ionizing continua, coupled to an equatorially concentrated BLR and a dusty screen with modest covering factor. Using inclination-dependent SEDs as input to Cloudy, we show that the extreme broad Halpha equivalent widths (EWs) of JWST LRDs are reproduced with global BLR covering factors of only 15%, consistent with standard Type 1 AGNs. Large Balmer EWs arise because self-shadowing suppresses the high-inclination optical continuum while the BLR is illuminated by an EUV-rich SED. Weak high-ionization lines follow from orientation-dependent suppression of the XUV/soft X-ray continuum toward equatorial directions, without requiring a fully enclosing gaseous "cocoon". With a gray attenuation law of AV = 2.8 along LRD-selected sightlines, the fiducial model matches the V-shaped UV-optical continua and large Balmer decrements; strong Balmer breaks occur only for the most obscured views. A compact equatorial dust component tied to the BLR and normalized by energy conservation intercepts and reradiates only a small fraction of Lbol, producing a modest hot-dust bump and far-IR/sub-mm emission consistent with current limits and implying small dust masses. The model unifies LRD and LBD observables via orientation, predicting correlated trends in Halpha EW, Balmer decrement, Balmer break, high-ionization line strengths, and IR emission.