# New insight on the nature of cosmic reionizers from the CEERS survey

**Authors:** S. Mascia, L. Pentericci, A. Calabrò, P. Santini, L. Napolitano, P. Arrabal Haro, M. Castellano, M. Dickinson, P. Ocvirk, J. S. W. Lewis, R. Amorín, M. Bagley, R. N. J. Cleri, L. Costantin, A. Dekel, S. L. Finkelstein, A. Fontana, M. Giavalisco, N. A. Grogin, N. P. Hathi  
**arXiv:** [2309.02219](https://arxiv.org/abs/2309.02219)  
**Date:** 2023-09-05  
**Summary page:** https://www.summarizepaper.com/en/paper/2309.02219v1/

## Key points

- The Epoch of Reionization (EoR) is a crucial period when galaxies began to increase in abundance and luminosity
- Galaxies emitted Lyman continuum (LyC) radiation, ionizing the surrounding intergalactic medium (IGM)
- Understanding cosmic reionizers during this epoch is still unclear
- Inability to directly measure LyC escape fraction ($f_{esc}$) due to IGM opacity
- Efforts made to identify indirect indicators in high-redshift galaxies that can predict $f_{esc}$
- Analysis of 62 spectroscopically confirmed star-forming galaxies at redshifts between 6 and 9 from CEERS survey
- Data from other JWST-ERS campaigns also included
- Measurements reveal compact size, blue color, and predicted LyC escape fraction of these galaxies
- Comparison with existing models provides insights into cosmic reionizers during EoR
- Low-mass galaxies with faint UV magnitudes likely played a significant role in reionization process
- Study contributes to understanding EoR and highlights importance of indirect indicators

## Summary

The Epoch of Reionization (EoR) is a crucial period in the history of the universe when galaxies began to increase in abundance and luminosity. As these galaxies emitted Lyman continuum (LyC) radiation, it started ionizing the surrounding neutral intergalactic medium (IGM). However, despite significant recent progress, the nature and role of cosmic reionizers during this epoch are still unclear. One major challenge in understanding these reionizers is the inability to directly measure their LyC escape fraction ($f_{esc}$) due to the opacity of the IGM. To overcome this challenge, many efforts have been made at low and intermediate redshifts to identify measurable indirect indicators in high-redshift galaxies that can predict their $f_{esc}$. In this study, researchers analyze 62 spectroscopically confirmed star-forming galaxies at redshifts between 6 and 9 from the Cosmic Evolution Early Release Science (CEERS) survey. They also include data from 12 sources with public data from other JWST-ERS campaigns. Using observations from NIRCam and NIRSpec instruments, the team measures various physical and spectroscopic properties of these high-redshift galaxies. The analysis reveals several key findings about star-forming galaxies at $6<z<9$. On average, these galaxies are compact in the rest-frame UV with a size of approximately 0.4 kiloparsecs ($r_e \sim $ 0.4 kpc). They also exhibit a blue color with a UV-$\beta$ slope of around -2.17. Additionally, their predicted LyC escape fraction is estimated to be about 0.13. Comparing these results to existing models and predictions provides valuable insights into the nature of cosmic reionizers during the EoR. Furthermore, an estimation of the ionizing budget suggests that low-mass galaxies with faint UV magnitudes below $M_{1500} = -18$, which are currently not characterized with JWST observations, likely played a significant role in the process of reionization. Overall, this study contributes to our understanding of the EoR by providing new insights into the properties and potential contributions of star-forming galaxies at high redshifts. The findings highlight the importance of indirect indicators in predicting LyC escape fraction and shed light on the role of low-mass galaxies in driving the process of reionization.