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

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.

Figures (3)

• Figure 1: Top: Distribution of $f_\mathrm{esc}$ for strong, weak, and non-leakers with and without WISE IR detections. Bottom: Distribution of O32 for the same categories. In each panel, individual galaxies are shown as jittered blue squares (IR-undetected) and red circles (IR-detected). For each category, the horizontal line denotes the median, and the box contains the middle 50% of the data. The vertical lines extend 1.5 times the height of the box.
• Figure 2: LyC detection fraction as a function of $\log$O32. The IR‑undetected systems (blue squares) show a rising LyC detection fraction with increasing O32 (blue dashed line), consistent with O32 tracing globally high ionization conditions. In contrast, the IR‑detected strong leakers (red dots) exhibit an approximately constant detection fraction across the full O32 range (red dashed line), indicating that their LyC escape is not strongly linked to the galaxy‑wide O32 ratio. The shaded region indicates the overall detection fraction for the combined sample. At low O32, the total detection fraction is dominated by the IR‑detected population, producing a weak trend in the combined sample.
• Figure 3: HST images for strong LyC leakers ($f_\mathrm{esc}>5\%$). Top: IR-detected strong leakers. Bottom: IR-undetected strong leakers.