We present measurements of stellar population properties of a newly discovered spectroscopically confirmed z=11.10−0.26+0.11, gravitationally lensed galaxy, using JWST NIRSpec PRISM spectroscopy and NIRCam imaging. The arc is highly magnified by the Bullet Cluster (magnification factor μ=14.0−0.3+6.2. It contains three star-forming components of which one is barely resolved and two are unresolved, giving intrinsic sizes of ≲10pc. The clumps also contain ~50% of the total stellar mass. The galaxy formed the majority of its stars ~150Myr ago (by z~14). The spectrum shows a pronounced damping wing, typical for galaxies deep in the reionisation era and indicating a neutral IGM at this line of sight. The intrinsic luminosity of the galaxy is 0.086−0.030+0.008L∗ (with L∗ being the characteristic luminosity for this redshift), making it the lowest luminosity spectroscopically confirmed galaxy at z>10 discovered to date.
@article{arxiv.2509.20446,
title = {Star Formation under a Cosmic Microscope: Highly magnified z = 11 galaxy behind the Bullet Cluster},
author = {Maruša Bradač and Jon Judež and Chris Willott and Gregor Rihtaršič and Nicholas S. Martis and Anishya Harshan and Giordano Felicioni and Yoshihisa Asada and Guillaume Desprez and Douglas Clowe and Anthony H. Gonzalez and Christine Jones and Brian C. Lemaux and Maxim Markevitch and Vladan Markov and Lamiya Mowla and Gaël Noirot and Annika H. G. Peter and Andrew Robertson and Ghassan T. E. Sarrouh and Marcin Sawicki and Tim Schrabback and Roberta Tripodi},
journal= {arXiv preprint arXiv:2509.20446},
year = {2025}
}