VENUS: When Red meets Blue -- A multiply imaged Little Red Dot with an apparent blue companion behind the galaxy cluster Abell 383

Miriam Golubchik, Lukas J. Furtak, Joseph F. V. Allingham, Adi Zitrin, Hollis B. Akins, Vasily Kokorev, Seiji Fujimoto, Abdurro'uf, Ricardo O. Amorín, Franz E. Bauer, Rachel Bezanson, Marusa Bradač, Larry D. Bradley, Gabriel B. Brammer, John Chisholm, Dan Coe, Christopher J. Conselice, Pratika Dayal, Miroslava Dessauges-Zavadsky, Jose M. Diego, Andreas L. Faisst, Qinyue Fei, Henry C. Ferguson, Steven L. Finkelstein, Brenda L. Frye, Mauro González-Otero, Jenny E. Greene, Yuichi Harikane, Tiger Yu-Yang Hsiao, Kohei Inayoshi, Yolanda Jiménez-Teja, Kirsten Knudsen, Anton M. Koekemoer, Ivo Labbé, Ray A. Lucas, Georgios E. Magdis, Jorryt Matthee, Matteo Messa, Rohan P. Naidu, Minami Nakane, Gaël Noirot, Richard Pan, Casey Papovich, Johan Richard, Massimo Ricotti, Luke Robbins, Daniel P. Stark, Fengwu Sun, Tommaso Treu, Roberta Tripodi, Eros Vanzella, Chris Willott, Rogier A. Windhorst

First listed 2025-12-01 | Last updated 2025-12-04

Abstract

We report the discovery of a doubly-imaged Little Red Dot (LRD) candidate behind the galaxy cluster Abell 383, which we dub A383-LRD1. Initially classified as a dropout galaxy in HST imaging with several ground-based emission line detections placing it at $z_{\mathrm{spec}}=6.027$, new JWST/NIRCam observations taken as part of the cycle 4 VENUS survey now reveal that the source consists of two underlying components: A red point-source with a V-shaped SED consistent with LRD selection criteria, and a nearby ($\sim 380$ pc) compact blue companion which was the main contributor to the previous rest-frame UV detections. Based on lensing symmetry and its SED, the LRD appears to lie at a similar redshift as well. The magnification of the two images of A383-LRD1 is $μ_{\mathrm{A}}=16.2\pm1.2$ and $μ_\mathrm{B}=9.0\pm0.6$, respectively, and the predicted time delay between them is $Δt_{\mathrm{grav}}=5.20\pm0.14$ yr ($\sim0.7$ yr in the rest-frame). After correcting for the lensing magnification, we derive an absolute magnitude of $M_{\mathrm{UV,LRD}}=-16.8\pm 0.3$ for the LRD, and $M_{\mathrm{UV,BC}}=-18.2\pm 0.2$ for the blue companion. We perform SED fits to both components, revealing the LRD to be best fitted with a black hole star (BH*) model and a substantial host galaxy, and the blue companion with an extremely young, emission-line dominated star-forming nebula. A383-LRD1 represents the second known multiply-imaged LRD detected to date, following A2744-QSO1, and to our knowledge, the first LRD system with a confirmed detection of [C $_{II}$]$\lambda158 \ μ$m emission from ALMA observations. Thanks to lensing magnification, this system opens a unique door to study the relation between a LRD, its host galaxy, and its environment, and represents a prime candidate for deep JWST spectroscopy and high-resolution ALMA follow-up observations.

Short digest

VENUS reports A383-LRD1, a doubly imaged Little Red Dot behind Abell 383 at z_spec=6.027, resolved by JWST/NIRCam into a red, point-like LRD with a V-shaped SED and a compact blue companion ~380 pc away that dominated past UV detections. Strong lensing yields μA=16.2±1.2 and μB=9.0±0.6 and predicts a Δt_grav=5.20±0.14 yr (~0.7 yr rest-frame), implying M_UV,LRD=-16.8±0.3 and M_UV,BC=-18.2±0.2 after demagnification. SED fits favor a BH* (black-hole-star) plus substantial host for the LRD, while the companion is an extremely young, emission-line dominated nebula with F356W/F444W excesses (Hβ+[O III], Hα). This is only the second known multiply imaged LRD and the first with confirmed ALMA [C II] 158 μm emission, offering a uniquely magnified laboratory for variability and LRD–host–environment connections.

Key figures to inspect

• Figure 1: Inspect the lensing geometry and critical curves—both images A and B show the blue companion and red LRD, and the model predicts a demagnified third image buried in the BCG, validating the multiply imaged interpretation and informing μ and time-delay estimates.
• Figure 2: Compare HST vs JWST cutouts—lack of ACS detections except F814W for the blue companion, and the LRD emerging toward redder NIRCam bands; note the F356W/F444W flux excesses consistent with Hβ+[O III] and Hα at z≈6, confirming the companion’s line-dominated nature.
• Figure 3: Read the SED fits—top panel’s BH*+host model reproduces the LRD’s V-shaped SED and yields the demagnified M_UV; bottom panel’s BEAGLE fit for the blue companion highlights extreme youth and strong nebular lines.
• Figure 4: Examine ALMA [C II] 158 μm contours—slight offset from the blue companion with the LRD within the 4σ contour; use this to assess whether [C II] traces the companion, the LRD host ISM, or a shared reservoir.