A sub-100 pc view at z~5 of a Multiply-Imaged Massive Quiescent Galaxy

Richard Pan, Danilo Marchesini, Joseph F. V. Allingham, Seiji Fujimoto, Adi Zitrin, Dan Coe, Vasily Kokorev, Lukas J. Furtak, Jacqueline Antwi-Danso, Yoshihisa Asada, Franz E. Bauer, Maruša Bradač, Larry D. Bradley, Chloe M. Cheng, Pratika Dayal, Andreas L. Faisst, Brenda L. Frye, Norman A. Grogin, Tiger Yu-Yang Hsiao, Gourav Khullar, Anton M. Koekemoer, Conor Larison, Ray A. Lucas, Vladan Markov, Nicholas S. Martis, Minami Nakane, Gaël Noirot, Johan Richard, Massimo Ricotti, Luke Robbins, Fengwu Sun, Francesco Valentino, Eros Vanzella, Chris Willott, Rogier A. Windhorst, Hiroto Yanagisawa, Anita Zanella

First listed 2026-09-24 | Last updated 2026-09-23

Abstract

Recent James Webb Space Telescope spectroscopic surveys reveal an abundance of rapidly assembled early galaxies in the first billion years. Cosmological simulations struggle to reproduce this population because models require a rapid, highly efficient conversion of baryons into stars followed by an abrupt cessation of star-formation, known as quenching, in the early Universe. Testing these theoretical models remains difficult because high-redshift field galaxies appear compact and unresolved. This lack of resolution makes it impossible to distinguish compaction-driven quenching from secular evolution. Here we present VENUS-CLJ0152-QG1, a massive post-starburst galaxy at $z=5.18\pm0.15$, with inferred low-levels of star-formation in the last 30 Myr. The foreground cluster CL J0152.7-1357 gravitationally lenses the system into three images with median magnifications of $μ\sim$ 7, 11, and 0.6. This geometry yields a physical resolution of $\sim 70$ pc, a factor of $\sim 7$ better than the JWST/NIRCam fundamental blurring limit (full-width half-maximum of $\sim$0.48 kpc at $z\sim5$). Our two-dimensional mapping reveals a half-light radius twice as large as expected, a central stellar mass surface density half a dex lower than field analogs, and off-center ionized gas emission. Together, these features show that VENUS-CLJ0152-QG1 abruptly ceased star formation in the absence of a compaction event or an obvious active galactic nucleus. Consequently, this galaxy shows that unresolved observations likely overestimate the global densities of early galaxies, and that theoretical models require alternative pathways to quench massive sources without relying on compaction or unobscured AGN.

Short digest

Pan et al. use cluster lensing by CL J0152.7-1357 to resolve the triply imaged post-starburst galaxy VENUS-CLJ0152-QG1 at z=5.18 on roughly 70 pc scales, far beyond the effective physical resolution available for comparable unlensed JWST targets. Spatially resolved mass, light, color, and medium-band line maps show an extended system with a half-light radius about twice that of field analogs, a central stellar-mass surface density lower by about 0.5 dex, and ionized-gas emission offset from the luminous core. The combination argues that this massive galaxy quenched abruptly without a preceding compact central buildup or an obvious unobscured AGN, implying that unresolved measurements can overstate early-galaxy densities and that models need quenching channels beyond compaction-driven evolution.

Key figures to inspect

• Figure 1. Use this overview to establish the three lensed images of VCQG1, their consistent spectral breaks and redshift solutions, and the rapidly declining recent star-formation histories that motivate its post-starburst classification.
• Figure 2. This is the central structural result: the lensing-resolved light, stellar-mass, and SFR-density maps show that VCQG1 is extended relative to field quiescent analogs and contains a localized star-forming enhancement offset from the light peak.
• Figure 3. The resolved rest-frame UV-optical color diagnostics and radial gradients test quenching geometry directly, disfavoring uniform or inside-out quenching interpretations for the source.
• Figure 4. This figure provides the clearest physical diagnostic for the paper's conclusion, showing that the medium-band emission-line excess is spatially separated from the stellar core; without lensing, it could be misidentified as a central starburst or AGN.