Influence of mergers on LyC escape of high redshift galaxies

TL;DR

This study shows that galaxy mergers significantly boost the escape of ionizing radiation in high-redshift galaxies, especially in low-mass systems, due to gas dynamics and star formation effects.

Contribution

It provides a detailed analysis of how galaxy mergers influence LyC escape fractions using cosmological simulations and a physical escape model.

Findings

Merger events increase LyC escape fraction from ~3% to 14%.

Low-mass galaxies are most affected by mergers in terms of LyC leakage.

Higher galaxy density correlates with increased LyC escape, partly due to merger frequency.

Abstract

Aims: We investigate the impact of galaxy mergers on the Lyman Continuum (LyC) radiation escape, fesc, from high-redshift galaxies. Methods: We post-process ~ 6e5 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 fesc ~ 3%, which increases to up to 14% immediately following a merger. The strongest effect can be observed in galaxies with stellar masses of ~ 1e7 Msun. 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 examine how proximity to other galaxies influences LyC escape, finding that galaxies with more neighbors 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 from mergers, because of their higher gas inflow, and consequent increase in the star formation rate. The increase in both mergers and gas inflow could contribute to low-mass galaxies ionizing proximity zones of high-z Ly-alpha leakers recently observed with JWST.