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

Abstract

Compact, star-forming galaxies with high star formation rate surface densities (${\Sigma }_{\text{SFR}}$) are often efficient Lyman continuum (LyC) emitters at $z\le 4.5$, likely as 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 investigate the influence of galaxy morphology on LyC production and escape at redshifts $5\le z\le 7$ using observations from various \textit{James Webb Space Telescope} (JWST) surveys. Our sample consists of 436 sources, which are predominantly low-mass ($\sim 10^{8.15}{M}_{\odot }$), star-forming galaxies with ionizing photon efficiency (${\xi }_{\mathrm{ion}}$) values consistent with canonical expectations. Since direct measurements of $f_{\mathrm{esc}}$ are not possible during the Epoch of Reionization (EoR), we predict $f_{\mathrm{esc}}$ 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 ($\sim 0.04$). Additionally, we assess the correlation between morphological features and LyC emission. Our findings indicate that neither ${\xi }_{\mathrm{ion}}$ nor the predicted $f_{\mathrm{esc}}$ values show a significant correlation with the presence of merger signatures. This suggests that in low-mass galaxies at $z\ge 5$, 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.

Submitted to A&A

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• Lyman Continuum escaping from in-situ formed stars in a tidal bridge at z = 3
• Extreme equivalent width-selected low-mass starbursts at $z=4-9$: insights into their role in cosmic reionization