Galaxy-LRD Strong Lenses: A Missing Population?

Zizhao He, Nan Li, Simon Dye, Xinzhong Er, Fuwen Shu

First listed 2026-08-05 | Last updated 2026-08-03

Abstract

The physical nature of Little Red Dots (LRDs) remains uncertain, although these abundant, compact, and red sources may offer important insights into early black-hole growth and galaxy formation. Strong gravitational lensing can magnify LRDs and spatially resolve their internal structure, thereby helping to discriminate among competing physical scenarios. However, no galaxy-scale strongly lensed LRD has yet been securely confirmed. To predict the abundance of such systems in current and future surveys and to guide dedicated searches, we present the first benchmark estimate of the detectable population of galaxy-scale lensed LRDs by combining literature-based LRD source models with a population of foreground early-type galaxy deflectors. Our Monte Carlo simulation spans $50~{\rm deg}^{2}$ and contains 270,713 LRDs and 5,460,841 deflectors. We predict idealized surface densities of $10.70\pm3.76~{\rm deg}^{-2}$ for doubles and $0.64\pm0.69~{\rm deg}^{-2}$ for quads. After accounting for the JWST point-spread function and survey limiting magnitudes, the detectable surface densities decrease to $3.70\pm1.89~{\rm deg}^{-2}$ and $0.52\pm0.58~{\rm deg}^{-2}$, respectively. For the de-duplicated $0.66~{\rm deg}^{2}$ footprint covered by COSMOS-Web, PRIMER-UDS, PRIMER-COSMOS, CEERS, JADES GOODS-S, and JADES GOODS-N, for which the reported limiting depths are combined through area-weighted averaging in flux space, the predicted probabilities of detecting no systems are $8.6\%$ for doubles and $70.8\%$ for quads.

Short digest

He et al. present the first forward-model benchmark for galaxy-scale strong lenses of little red dots, pairing a Kokorev et al.-based LRD UV luminosity function with a mock population of early-type galaxy deflectors across 50 deg². Their simulation predicts detectable JWST surface densities of 3.70±1.89 deg⁻² for doubles and 0.52±0.58 deg⁻² for quads after PSF-resolution and depth cuts, implying that lensed LRDs should be present but rare in current blank-field data. For the combined, de-duplicated 0.66 deg² footprint of major JWST surveys, a null result is relatively unlikely for doubles (8.6%) but unsurprising for quads (70.8%), motivating targeted searches for resolved systems that could separate compact nuclear light from host-galaxy emission.

Key figures to inspect

• Figure 1. This figure establishes the population inputs behind the forecast: the adopted two-bin LRD UV luminosity function and the sizes, shapes, and velocity dispersions of the foreground early-type deflectors. It is essential context for interpreting the predicted lens yields as a forward-model result tied to specific source and lens demographics.
• Figure 2. This is the paper’s central forecast figure, connecting lensed-image magnitudes, lens and source redshifts, image separations, JWST resolution, and expected counts versus survey area. The cumulative-area panel most directly explains why existing JWST fields could plausibly have missed quads while a continued null detection of doubles becomes increasingly informative.
• Figure 3. This figure quantifies a practical observational caveat beyond nominal PSF and depth cuts: contamination from the foreground lens galaxy at the positions of lensed LRD images. The mock image stamps show why candidate searches and follow-up modeling must account for deflector light even when the lensed source is formally detectable.