In the early Universe, extreme-UV photons produced in young stars in the first galaxies somehow found their way out of these galaxies to reionize the then-neutral Intergalactic Medium. Star-forming galaxies are rich in interstellar neutral Hydrogen, which absorbs ionizing photons, so their escape is contingent on the existence of pathways out of the galaxy with little or no neutral gas. Which conditions and mechanisms give rise to these pathways is a topic of intense research in extragalactic astronomy.
Mapping and understanding these pathways require us to observe both the ionizing emission and the interstellar gas on scales ranging from a few parsec and up to the scale of the entire galaxy. Such studies are made difficult by a number of technical and astrophysical challenges: If the galaxies are too close, it becomes very difficult to study the ionizing emission, and if they are too distant, the IGM will absorb it, and the sheer distance forbid the necessary amount of detail.
An exciting path forward for this is the study of ionizing galaxies at redshift 2-4 magnified by gravitational lensing. At these redshifts, it is technically viable to observe the ionizing emission with Hubble, while the diagnostic emission lines we ususally use to study the ISM all fall within the most sensitive wavelength ranges of JWST. Together with the magnification from gravitational lensing, this allows us to study ionizing leaker galaxies at cosmological distances at a level of detail usually reserved for the local Universe, but without the difficulties of the local Universe. In this colloquium, I will describe a HST/JWST pilot study of such a gravitationall lensed ionizing leaker galaxy, the Sunburst Arc, and show some tentative results of what we can learn from it about exactly how these pathways have been created and under which conditions we can expect to find them.