A Lyman continuum analysis of ∼100 galaxies at z_spec∼ 3 in the Abell 2744 cluster field

¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
² Department of Astronomy, School of Physics, Peking University, Beijing 100871, China
³ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China
⁴ Institute of Science and Technology Austria (ISTA), Am Campus 1, A-3400 Klosterneuburg, Austria
⁵ INAF – Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
⁶ Center for Astrophysical Sciences, William H. Miller III Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
⁷ School of Astronomy and Space Science, University of Chinese Academy of Sciences (UCAS), Beijing 100049, China
⁸ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
⁹ Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing 102206, China
¹⁰ Dipartimento di Fisica, Università di Roma Sapienza, Città Universitaria di Roma – Sapienza, Piazzale Aldo Moro, 2, 00185 Roma, Italy
¹¹ Department of Physics & Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA
¹² IPAC, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁴ University of Ljubljana, Faculty of Mathematics and Physics, Jadranska ulica 19, SI-1000 Ljubljana, Slovenia
¹⁵ Department of Physics and Astronomy, University of California Davis, 1 Shields Avenue, Davis, CA 95616, USA
¹⁶ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, I-40129 Bologna, Italy
¹⁷ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218 Hawthorn, VIC 3122, Australia
¹⁸ School of Physics, The University of Melbourne, VIC 3010, Australia
¹⁹ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy

^★ Corresponding author: yuchenliu.pku@gmail.com

Received: 15 July 2025
Accepted: 21 October 2025

Abstract

Identifying Lyman continuum (LyC) leakers at intermediate redshifts is crucial for understanding the properties of cosmic reionizers because the opacity of the intergalactic medium (IGM) prevents the direct detection of LyC emission from sources during the Epoch of Reionization (EoR). In this study, we confirm two new LyC candidate leakers at z ∼ 3 in the Abell 2744 cluster field, with absolute escape fractions (f_esc) of 0.83_−0.80^+0.15 and 0.74_−0.70^+0.23, respectively. The LyC emission was detected using HST/WFC3/F275W and F336W imaging. These two candidate leakers appear to be faint (M_UV = −17.61 ± 0.06 and −18.22 ± 0.10), exhibit blue UV continuum slopes (β = −2.43 ± 0.05 and −1.92 ± 0.09), have low masses (M_★ ∼ 10^{7.51 ± 0.03} and 10^{7.17 ± 0.15} M_⊙) and Lyα equivalent widths of 90 ± 3 Å and 28 ± 12 Å, respectively. These two LyC candidate leakers were detected in a catalog of 91 spectroscopically confirmed sources using public spectra from the JWST and/or MUSE. We also analyzed properties that were proposed as indirect indicators of LyC emission, such as Lyα, the O32 ratio, and M_★. We created a galaxy subsample that was selected according to these properties, stacked the LyC observations of this subsample, and assessed the limits of the escape fractions in the stacks. We aim to enhance our understanding of LyC escape mechanisms and improve our predictions of the LyC f_esc during the EoR by analyzing the individual candidates and the stacks in the context of the currently limited sample of known LyC leakers at z ∼ 3.