# The Lyman Continuum Escape Fraction of Star-forming Galaxies at $2.4\lesssim z\lesssim3.7$ from UVCANDELS

**Authors:** Xin Wang, Harry I. Teplitz, Brent M. Smith, Rogier A. Windhorst, Marc Rafelski, Vihang Mehta, Anahita Alavi, Gabriel Brammer, James Colbert, Norman Grogin, Nimish P. Hathi, Anton M. Koekemoer, Laura Prichard, Claudia Scarlata, Ben Sunnquist, Pablo Arrabal Haro, Christopher Conselice, Eric Gawiser, Yicheng Guo, Matthew Hayes  
**arXiv:** [2308.09064](https://arxiv.org/abs/2308.09064)  
**Date:** 2023-08-17  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.09064v1/

## Key points

- The UVCANDELS survey aims to study the Lyman continuum escape fraction of star-forming galaxies at redshifts 2.4 ≤ z ≤ 3.7
- The survey utilizes the Hubble Space Telescope and imaging from the Wide-Field Camera 3 Ultraviolet and Visible light F275W, along with coordinated parallel Advanced Camera for Surveys F435W imaging
- The survey focuses on four premier extragalactic survey fields: GOODS-N, GOODS-S, EGS, and COSMOS
- The paper provides an overview of the key science drivers of the UVCANDELS Treasury Program in Section 2
- Observing strategy and data reduction details are discussed in Section 3
- Galaxy sample selection with spectroscopic redshifts is explained in Section 4
- Image stacking techniques are described and results are presented in Section 5
- Five individual LyC leaker candidates with estimated escape fractions above 60% are reported using Monte Carlo analysis
- A robust stacking method is developed to analyze a total of 85 non-detection galaxies, providing tight upper limits below 6% for most stacks
- A stack of 32 emission-line galaxies shows tentative LyC leakage detected at a significance level of 2.9-sigma, indicating an escape fraction of 5.7% at z ~ 2.65
- This finding supports the role these galaxies play in contributing to cosmic reionization and maintaining UV ionization background levels

## Summary

The UltraViolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) survey is a Hubble Space Telescope (HST) Cycle-26 Treasury Program that aims to study the Lyman continuum (LyC) escape fraction ($f_{\rm esc}$) of star-forming galaxies at redshifts $2.4\lesssim z\lesssim3.7$. The survey utilizes the Wide-Field Camera 3 Ultraviolet and Visible light F275W imaging, along with coordinated parallel Advanced Camera for Surveys F435W imaging, on four premier extragalactic survey fields: GOODS-N, GOODS-S, EGS, and COSMOS. In this paper, we present a comprehensive overview of the key science drivers of the UVCANDELS Treasury Program in Section 2. We discuss the observing strategy and data reduction details in Section 3, followed by an explanation of our galaxy sample selection with spectroscopic redshifts in Section 4. In Section 5, we describe our image stacking techniques and present the results. To infer the LyC escape fraction ($f_{\rm esc}$), we conduct an extensive search for LyC emission and perform a stacking analysis on a population of star-forming galaxies with secure redshifts. This analysis benefits from high-quality spectroscopic redshift catalogs compiled from archival ground-based data and HST slitless spectroscopy. We report five individual LyC leaker candidates with estimated $f_{\rm esc}^{\rm rel}\gtrsim60\%$ using detailed Monte Carlo analysis of intergalactic medium attenuation. Furthermore, we develop a robust stacking method to analyze a total of 85 non-detection galaxies in the redshift range $z\in[2.4,3.7]$. Most stacks provide tight 2-$\sigma$ upper limits below $f_{\rm esc}^{\rm rel}<6\%$. However, a stack of 32 emission-line galaxies shows tentative LyC leakage detected at 2.9-$\sigma$, indicating $f_{\rm esc}^{\rm rel}=5.7\%$ at $z \sim 2.65$. This finding supports the significant role such galaxies play in contributing to cosmic reionization and maintaining UV ionization background levels. The UVCANDELS survey has provided extensive UVIS imaging in four premier HST deep-wide survey fields enabling various scientific explorations such as studying structural evolution of galaxies; tracing evolution of star formation; gas and dust content; investigating role environment plays in low mass star forming galaxy evolution; probing decay rate of star formation in massive early type galaxies; minor mergers; constraining escape fraction ionizing radiation from high redshift galaxies to better understand how star forming galaxies reionized Universe etc..