Influence of mergers on the Lyman continuum escape of high-redshift galaxies

¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
² Scuola Normale Superiore, Piazza dei Cavalieri 7, I-50126 Pisa, Italy

^⋆ Corresponding author: ivan.kostyuk@sns.it

Received: 5 December 2024
Accepted: 13 August 2025

Abstract

Aims. We investigated the impact of galaxy mergers on the Lyman continuum (LyC) radiation escape, f_esc, from high-redshift galaxies.

Methods. We post-processed ≈5 × 10⁵ galaxies (redshift 5.2 <  z <  10) extracted from the TNG50 cosmological simulation using a physically motivated analytic model for LyC escape.

Results. Galaxies that have not experienced a merger for the last ≈700 Myr have an average f_esc ∼ 3%, which increases up to 14% immediately following a merger. The strongest effect can be observed in galaxies with stellar masses of ∼10⁷ M_⊙. We attribute the increase in the escape fraction to two main factors: (i) accretion of metal-poor gas onto the central region of a galaxy, which feeds star formation and LyC emission, and (ii) displacement of neutral gas relative to star-forming regions, which reduces the optical depth to LyC photons. We additionally examined how proximity to other galaxies influences LyC escape, finding that galaxies with more neighbours tend to have more frequent mergers, and thus a higher LyC leakage. However, galaxies in overdense regions tend to have a larger LyC escape fraction independently of mergers because of their higher gas inflow, and consequent increase in the star formation rate. The increase in mergers and in gas inflow could contribute to low-mass galaxies ionising proximity zones of high-z Lyα leakers recently observed with JWST.