James Webb Space Telescope Feed Post

UNCOVER-z12 | UNCOVER: Illuminating the Early Universe -- JWST/NIRSpec Confirmation of z > 12 Galaxies

Abstract: Observations of high-redshift galaxies provide a critical direct test to the theories of early galaxy formation, yet to date, only four have been spectroscopically confirmed at z>12. Due to strong gravitational lensing over a wide area, the galaxy cluster field Abell~2744 is ideal for searching for the earliest galaxies. Here we present JWST/NIRSpec observations of two galaxies: a robust detection at zspec=12.393+0.004-0.001, and a plausible candidate at zspec=13.079+0.013-0.001. The galaxies are discovered in JWST/NIRCam imaging and their distances are inferred with JWST/NIRSpec spectroscopy, all from the JWST Cycle 1 UNCOVER Treasury survey. Detailed stellar population modeling using JWST NIRCam and NIRSpec data corroborates the primeval characteristics of these galaxies: low mass (~108 M?), young, rapidly-assembling, metal-poor, and star-forming. Interestingly, both galaxies are spatially resolved, having lensing-corrected rest-UV effective radii on the order of 300-400 pc, which are notably larger than other spectroscopically confirmed z?12 systems. The observed dynamic range of z?12 size spans over an order of magnitude, implying a significant scatter in the size-mass relation at early times. Deep into the epoch of reionization, these discoveries elucidate the emergence of the first galaxies.