Tidally offset neutral gas in Lyman continuum emitting galaxy Haro 11

Around 400 million years after the Big Bang, the ultraviolet emission from star-forming galaxies reionized the Universe. Ionizing
radiation (Lyman Continuum, LyC) is absorbed by cold neutral hydrogen gas (Hi) within galaxies, hindering the escape of LyC
photons. Since the Hi reservoir of LyC emitters has never been mapped, major uncertainties remain on how LyC photons escape
galaxies and ionize the intergalactic medium. We have directly imaged the neutral gas in the nearby reionization-era analog
galaxy Haro 11 with the 21cm line to identify the mechanism enabling ionizing radiation escape. We find that merger-driven
interactions have caused a bulk offset of the neutral gas by about 6 kpc from the center of the galaxy, where LyC emission
production sites are located. This could facilitate the escape of ionizing radiation into our line of sight. Galaxy interactions can
cause both elevated LyC production and large-scale displacement of Hi from the regions where these photons are produced.
They could contribute to the anisotropic escape of LyC radiation from galaxies and the reionization of the Universe. We argue
for a systematic assessment of the effect of environment on LyC production and escape.