Two Lyman Continuum Escape Mechanisms at Play in $z\sim0.3$ galaxies Revealed by Infrared Observations

TL;DR

This study reveals two distinct mechanisms for Lyman continuum photon escape in local galaxies, showing that both low-mass, dust-poor and more massive, dusty galaxies can contribute to cosmic reionization.

Contribution

It identifies and characterizes two different IR-bright and IR-undetected pathways for LyC escape in local galaxies, expanding understanding of reionization sources.

Findings

IR-undetected leakers have high O32 ratios and low stellar masses.

IR-bright leakers have low O32 ratios but high escape fractions.

Both populations resemble high-redshift LyC leakers, indicating multiple escape pathways.

Abstract

We investigate the infrared (IR) properties of a sample of local star-forming galaxies using the WISE data. Focusing on the 20 confirmed strong Lyman continuum (LyC) leakers ($f_\mathrm{esc}>5\%$) included in this sample, we find that the IR detection separates these strong LyC leakers into two populations. The IR-undetected strong leakers in our sample exhibit high [OIII]5007/[OII]3725,3727 (O32) ratios, blue UV slopes, and low stellar masses, consistent with the classical density-bound scenario where the entire ISM is highly ionized. However, IR-bright strong leakers display unexpectedly low O32 ratios while maintaining a substantial escape fraction of $f_{\text{esc}} \sim 12\%$. They also have higher stellar masses and redder UV slopes, similar to weak or non-leakers, along with low nebular extinction, suggesting that the LyC photons are likely to escape through low-column-density channels in a high-density, ionization-bound clumpy medium. Morphologically, these two populations echo the compact starburst and merger-driven LyC leakers observed at $z \sim 3$, indicating that both escape pathways coexist across cosmic time. Our results demonstrate that efficient LyC escape is not limited to the lowest-mass, dust-poor dwarfs but can also occur in more massive, dusty environments, highlighting the potential contribution from dusty systems and posing new questions about the actual dominance of different galaxy populations during the Epoch of Reionization.