(Re)solving the complex multi-scale morphology and V-shaped SED of a newly discovered strongly-lensed Little Red Dot in Abell 383

Josephine F. W. Baggen, Pieter van Dokkum, Ivo Labbé, Gabriel Brammer

First listed 2025-12-02 | Last updated 2025-12-02

Abstract

We present a luminous Little Red Dot (LRD) at $z=6.027$, doubly imaged by the galaxy cluster Abell 383 and observed with JWST/NIRCam. The source shows the characteristic "V-shaped" SED and pronounced Balmer break that define the LRD population. Owing to its large magnifications, $μ\sim11$ for image S1 and $μ\sim7$ for S2, the system is exceptionally bright and highly stretched, providing a rare, spatially resolved view of an LRD. The images reveal a complex morphology with a compact red dot, a spatially offset blue dot, and faint emission bridging and surrounding the two. After correcting for lensing, we find that both dots are extremely small but resolved, with rest-frame UV sizes of $\sim 20$ pc (red) and $\sim60$ pc (blue). These compact dots are embedded in a more extended, line-dominated cloud traced most clearly in F356W ([OIII]+H$β$), which reaches scales of order $\sim$1 kpc. SED decomposition shows that the blue component has a flat UV continuum consistent with a young stellar population, whereas the red component has a steep red SED that can be interpreted as either an evolved stellar population with high stellar mass ($\log M_\star/M_\odot>10$) or a reddened AGN. If this object is representative of the LRD population, our results imply that the V-shaped SEDs of LRDs do not arise from individual compact sources but instead from the superposition of two physically distinct components. Separated by only $\sim300$ pc in the source plane, these components would blend into a single compact source in unlensed observations with the canonical LRD colors. This system therefore provides a rare opportunity to resolve the internal structure of an LRD and to gain direct insight into the physical nature of this population.

Short digest

A luminous Little Red Dot at z=6.027 is doubly imaged by Abell 383 (μ≈11 for S1, μ≈7 for S2), enabling a rare spatially resolved look at an LRD with a V‑shaped SED. The source breaks into a compact red dot and a spatially offset blue dot separated by ~300 pc, embedded in an extended, line‑dominated cloud traced most clearly in F356W ([OIII]+Hβ) out to ~1 kpc. Lens-corrected sizes are extreme yet resolved: ~20 pc (red) and ~60 pc (blue); SED decomposition favors a young stellar population for the blue component and either an evolved, massive (log M⋆/M⊙>10) population or a reddened AGN for the red component. If representative, this implies LRD V‑shapes arise from the superposition of two physically distinct components that would blend into a single compact source without lensing.

Key figures to inspect

• Fig. 1: Cluster‑scale RGB and multi‑band cutouts locating S1/S2; use these to assess image parities, stretching, and how the red/blue colors emerge across filters in each lensed image.
• Fig. 2: SEDs of S1 and S2 showing the Lyman and Balmer breaks and the characteristic V‑shape; verify that S1/S2 flux ratios follow the lensing magnification and inspect the μ‑corrected intrinsic SED.
• Fig. 3: RGB stamps (F200W/F150W/F115W) isolating the internal structure; measure the centroid offset between the compact red dot and blue dot and identify the bridge emission that links them.
• Fig. 4: GALFIT model/residual panels demonstrating both components are resolved and tiny; read off which bands drive the ~20 pc (red) vs ~60 pc (blue) sizes and confirm minimal residuals supporting the decomposition.