The Importance of Dust Distribution in Ionizing-photon Escape: NIRCam and MIRI Imaging of a Lyman Continuum-emitting Galaxy at z ~ 3.8

Abstract

We present deep JWST/NIRCam and MIRI imaging of Ion1, a previously confirmed Lyman Continuum (LyC)-emitting galaxy at $z_{spec}=3.794$. Together with existing HST imaging, these new observations from the JADES program enable a joint analysis of Ion1's LyC, rest-frame UV, stellar, and dust emission with unprecedented detail. We report the first detection of dust emission at rest-frame $\sim 3\mu$m in a high-redshift LyC-emitting galaxy using MIRI/F1500W. Our analysis suggests a porous distribution of dust in Ion1, with regions exhibiting evidence of dust deficit coinciding both with LyC-emitting regions and with the peak of H$\alpha$ emission. Furthermore, multi-band NIRCam imaging reveals a strong FUV-to-optical color gradient, where LyC-emitting regions appear significantly bluer than the rest of Ion1. Spatially resolved SED fitting confirms that this color gradient is primarily driven by spatially varying dust attenuation. Together, these findings suggest that Ion1's LyC emission originates from a compact star-forming complex near its stellar-light centroid, where stellar feedback carves out low HI column density channels, facilitating LyC escape. However, only a fraction of these LyC photons - specifically those along sightlines with minimal HI obscuration - ultimately escape and reach observers. This work underscores the critical role of dust and neutral gas geometry in shaping LyC escape in galaxies at high redshifts. Anisotropic LyC escape may be a common feature in the early Universe, which must be properly incorporated to constrain the Epoch of Reionization.

Accepted for publication in ApJ Letters. 23 pages, 11 figures

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Cited by in corpus (4)

• The Lyman-alpha and Continuum Origins Survey. I. Survey description and Ly$\alpha$ imaging
• The Lyman-alpha and Continuum Origins Survey II: the connection between the escape of ionizing radiation and Lyman-alpha halos in star-forming galaxies
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• REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization