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

**Authors:** Bingjie Wang, Seiji Fujimoto, Ivo Labbe, Lukas J. Furtak, Tim B. Miller, David J. Setton, Adi Zitrin, Hakim Atek, Gabriel Brammer, Rachel Bezanson, Joel Leja, Pascal A. Oesch, Sedona H. Price, Iryna Chemerynska, Sam E. Cutler, Pratika Dayal, Pieter van Dokkum, Andy D. Goulding, Jenny E. Greene, Y. Fudamoto  
**arXiv:** [2308.03745](https://arxiv.org/abs/2308.03745)  
**Date:** 2023-08-07  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.03745v1/

## Key points

- Observations of high-redshift galaxies are crucial for testing theories of early galaxy formation
- The galaxy cluster field Abell 2744 provides an ideal opportunity to search for the earliest galaxies
- Two galaxies at redshifts $z=12.40$ and $z=13.08$ were observed using the James Webb Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec)
- These galaxies were initially discovered through JWST/NIRCam imaging and their distances were determined using JWST/NIRSpec spectroscopy
- Detailed stellar population modeling confirms that these galaxies exhibit primeval characteristics, with low masses, young and rapidly forming stars, low metallicity, and active star-forming activity
- Both galaxies are spatially resolved with lensing-corrected rest-UV effective radii ranging from 300 to 400 parsecs
- The sizes of these galaxies suggest significant scatter in the size-mass relation during early cosmic times
- These discoveries provide valuable insights into the emergence of the first galaxies deep into the epoch of reionization
- They contribute to our understanding of early galaxy formation and evolution, as well as the structure and dynamics of the early universe.

## Summary

Observations of high-redshift galaxies are crucial for testing theories of early galaxy formation. The galaxy cluster field Abell 2744 provides an ideal opportunity to search for the earliest galaxies. In this study, the authors present observations from the James Webb Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec) of two galaxies: one with a robust detection at $z=12.40$ and another as a plausible candidate at $z=13.08$. These galaxies were initially discovered through JWST/NIRCam imaging and their distances were determined using JWST/NIRSpec spectroscopy as part of the JWST Cycle 1 UNCOVER Treasury survey. Detailed stellar population modeling using data from both JWST NIRCam and NIRSpec instruments confirms that these galaxies exhibit primeval characteristics. They have low masses on the order of $10^8$ solar masses, are young and rapidly forming stars, have low metallicity, and show active star-forming activity. Notably, both galaxies are spatially resolved with lensing-corrected rest-UV effective radii ranging from 300 to 400 parsecs. These sizes are larger than those typically observed in other systems at redshifts greater than 10 ($z>10$), suggesting significant scatter in the size-mass relation during early cosmic times. The discoveries presented in this study provide valuable insights into the emergence of the first galaxies deep into the epoch of reionization. By expanding our understanding of early galaxy formation and evolution, these observations contribute to our knowledge of the early universe's structure and dynamics.