# UNCOVER: A NIRSpec Census of Lensed Galaxies at z=8.50-13.08 Probing a High AGN Fraction and Ionized Bubbles in the Shadow

**Authors:** Seiji Fujimoto, Bingjie Wang, John Weaver, Vasily Kokorev, Hakim Atek, Rachel Bezanson, Ivo Labbe, Gabriel Brammer, Jenny E. Greene, Iryna Chemerynska, Pratika Dayal, Anna de Graaff, Lukas J. Furtak, Pascal A. Oesch, David J. Setton, Sedona H. Price, Tim B. Miller, Christina C. Williams, Katherine E. Whitaker, Adi Zitrin  
**arXiv:** [2308.11609](https://arxiv.org/abs/2308.11609)  
**Date:** 2023-08-22  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.11609v1/

## Key points

- Study using JWST NIRSpec prism spectroscopy to observe gravitationally lensed galaxies at redshifts > 9
- Focus on confirming redshifts and investigating properties of high-redshift galaxies
- Confirmation of source redshift for ten galaxies in the range of z=8.50-13.08
- Ultraviolet (UV) luminosities down to $M_{\rm UV}=-17.3$
- 100% confirmation rate for candidates with redshifts > 9
- Caution regarding offset between emission lines and Lyman-alpha break estimates
- Lower limits on rest-frame UV luminosity function (LF) derived at redshifts ~9-12, consistent with recent photometric measurements
- Identification of active galactic nucleus (AGN) systems based on X-ray emission, broad line H$\beta$, high ionization line detections, and excess in UVLF
- Confirmation of one UV-luminous source at same redshift as dusty broad-line AGN with physical separation of 380 kpc in source plane

## Summary

In this study, the authors present the results of their observations using the JWST NIRSpec prism spectroscopy to study gravitationally lensed galaxies at redshifts greater than 9. These galaxies were found behind the massive galaxy cluster Abell 2744 as part of the UNCOVER Cycle 1 Treasury Program. The main focus of this study is to confirm the redshifts of these high-redshift galaxies and investigate their properties. The authors confirm the source redshift for ten galaxies in the range of z=8.50-13.08 by detecting emission lines and/or the Lyman-alpha break feature. These confirmed sources have ultraviolet (UV) luminosities down to $M_{\rm UV}=-17.3$. The confirmation rate for candidates with redshifts greater than 9 reported in a previous study by Atek et al. (2023) is found to be 100%. When comparing redshift estimates obtained from emission lines and those obtained from the Lyman-alpha break alone using prism, it is found that there can be an offset of up to $\pm0.2$, raising caution in designing future follow-up spectroscopy for sources that rely solely on the Lyman-alpha break. Using both confirmed sources from UNCOVER and literature, lower limits on the rest-frame UV luminosity function (LF) are derived at redshifts approximately between 9 and 12. These lower limits are found to be consistent with recent photometric measurements. The authors also identify several active galactic nucleus (AGN) systems based on X-ray emission, broad line H$\beta$, high ionization line detections (such as NIV]1487 and CIV1549), and excess in UVLF, suggesting that AGNs may contribute significantly to the high abundance of galaxies at redshifts greater than 9 claimed in recent photometric studies. One UV-luminous source is confirmed to be at the same redshift as a dusty broad-line AGN with a physical separation of 380 kpc in the source plane; these two sources show blueward Lyman-alpha line or continuum emission, indicating that they reside in the same ionized bubble with a radius of $7.56\pm0.10$ pMpc.