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Arxiv: UNCOVER: Illuminating the Early Universe -- JWST/NIRSpec Confirmation of z > 12 Galaxies Published: 8/7/2023 8:52:11 PM Updated: 10/10/2023 7:26:41 PM

Paper abstract: Observations of high-redshift galaxies provide a critical direct test to thetheories of early galaxy formation, yet to date, only three have beenspectroscopically confirmed at z>12. Due to strong gravitational lensing overa wide area, the galaxy cluster field A2744 is ideal for searching for theearliest galaxies. Here we present JWST/NIRSpec observations of two galaxies: arobust detection at z_{\rm spec} = 12.393^{+0.004}_{-0.001}, and a plausiblecandidate at z_{\rm spec} = 13.079^{+0.013}_{-0.001}. The galaxies arediscovered in JWST/NIRCam imaging and their distances are inferred withJWST/NIRSpec spectroscopy, all from the JWST Cycle 1 UNCOVER Treasury survey.Detailed stellar population modeling using JWST NIRCam and NIRSpec datacorroborates the primeval characteristics of these galaxies: low mass (~10^8~{\rm M_\odot}), young, rapidly-assembling, metal-poor, and star-forming.Interestingly, both galaxies are spatially resolved, having lensing-correctedrest-UV effective radii on the order of 300-400 pc, which are notably largerthan other spectroscopically confirmed systems at similar redshifts. Theobserved dynamic range of z \gtrsim 10 sizes spans over 1 order of magnitude,implying a significant scatter in the size-mass relation at early times. Deepinto the epoch of reionization, these discoveries elucidate the emergence ofthe first galaxies.