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| Paper: |
How Do Ionizing Photons Escape from Star-Forming Galaxies? |
| Monograph: |
10, HWO25 Proceedings Part I: Community Science Case Development Documents |
| Page: |
179 |
| Authors: |
Cody Carr; Renyue Cen; Sophia Flury; M. S. Oey; Stephan McCandliss; Allison Strom |
| DOI: |
10.26624/KTXA9762 |
| Abstract: |
The Epoch of Reionization marks the last major phase transition in the early Universe, during which
the majority of neutral hydrogen once filling the intergalactic medium was ionized by the first galaxies.
The James Webb Space Telescope is now identifying promising galaxy candidates capable of producing
sufficient ionizing photons to drive this transformation. However, the fraction of these photons that escape
into intergalactic space—the escape fraction—remains highly uncertain. Stellar feedback is thought to play
a critical role in carving low-density channels that allow ionizing radiation to escape, but the dominant
mechanisms, their operation, and their connection to observable signatures are not well understood. Local
analogs of high-redshift galaxies offer a powerful alternative for studying these processes, since ionizing
radiation is unobservable at high redshift due to intergalactic absorption. However, current UV space-based
instrumentation lacks the spatial resolution and sensitivity required to fully address this problem. The core
challenge lies in the multiscale nature of LyC escape: ionizing photons are generated on scales of 1–100 pc
in super star clusters but must traverse the circumgalactic medium which can extend beyond 100 kpc. A UV
integral field unit (IFU) spectrograph capable of resolving galaxies across these scales is necessary—and
uniquely achievable with the proposed Habitable Worlds Observatory. In this article, we outline the scientific
motivation, observables, and observational capabilities needed to make progress on these fundamental
questions. |
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