Little impact of mergers and galaxy morphology on the production and escape of ionizing photons in the early Universe

¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33 00078 Monteporzio Catone, Italy
² Institute of Science and Technology Austria (ISTA), Am Campus 1 A-3400, Klosterneuburg, Austria
³ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁴ Center for Astrophysics, Harvard & Smithsonian, Cambridge, MA 02138, USA
⁵ Department of Physics and Astronomy, Williams College, Williamstown, MA 01267, USA
⁶ Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004 18080 Granada, Spain
⁷ European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n 28692 Villanueva de la Cañada, Madrid, Spain
⁸ Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
⁹ Institute for Computational and Data Sciences, The Pennsylvania State University, University Park, PA 16802, USA
¹⁰ Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
¹¹ Centro de Astrobiología, Consejo Superior de Investigaciones Científicas, Madrid, Spain
¹² Department of Physics, 196A Auditorium Road, Unit 3046, University of Connecticut, Storrs, CT 06269, USA
¹³ University of Massachusetts Amherst, 710 North Pleasant Street, Amherst, MA 01003-9305, USA
¹⁴ NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
¹⁵ University of Louisville, Department of Physics and Astronomy, 102 Natural Science Building, Louisville, KY 40292, USA
¹⁶ Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
¹⁷ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX, USA
¹⁸ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n-La Laguna, Spain
¹⁹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁰ Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA
²¹ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²² Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, UK
²³ Institute of Space Sciences and Astronomy, University of Malta, Msida MSD 2080, Malta
²⁴ The University of Texas, Austin, TX, USA

^⋆ Corresponding author: sara.mascia@ista.ac.at

Received: 15 January 2025
Accepted: 7 July 2025

Abstract

Compact, star-forming galaxies with high star formation rate surface densities (Σ_SFR) are often efficient Lyman continuum (LyC) emitters at z ≤ 4.5, likely because intense stellar feedback creates low-density channels that allow photons to escape. Irregular or disturbed morphologies, such as those resulting from mergers, can also facilitate LyC escape by creating anisotropic gas distributions. We investigated the influence of galaxy morphology on LyC production and escape at redshifts 5 ≤ z ≤ 7 using observations from various James Webb Space Telescope (JWST) surveys. Our sample consists of 436 sources, which are predominantly low-mass (∼10^8.15 M_⊙), star-forming galaxies with ionizing photon efficiency (ξ_ion) values consistent with canonical expectations. Since direct measurements of f_esc are not possible during the Epoch of Reionization (EoR), we predicted f_esc for high-redshift galaxies by applying survival analysis to a subsample of LyC emitters from the Low-Redshift Lyman Continuum Survey (LzLCS), selected to be direct analogs of reionization-era galaxies. We find that these galaxies exhibit, on average, modest predicted escape fractions (∼0.04). In addition, we evaluated the correlation between morphological features and LyC emission. Our findings indicate that neither ξ_ion nor the predicted f_esc values show a significant correlation with the presence of merger signatures. This suggests that in low-mass galaxies at z ≥ 5, strong morphological disturbances are not the primary mechanism driving LyC emission and leakage. Instead, compactness and star formation activity likely play a more pivotal role in regulating LyC escape.