Star Formation under a Cosmic Microscope: Highly magnified z = 11 galaxy behind the Bullet Cluster

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 $\mu =14.0_{-0.3}^{+6.2}$. It contains three star-forming components of which one is barely resolved and two are unresolved, giving intrinsic sizes of $\lesssim 10pc$. 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 $0.086_{-0.030}^{+0.008}{L}^{\ast }$ (with $L^{\ast }$ being the characteristic luminosity for this redshift), making it the lowest luminosity spectroscopically confirmed galaxy at $z>10$ discovered to date.