Tidally offset neutral gas in Lyman continuum emitting galaxy Haro 11

TL;DR

This study maps neutral hydrogen in the galaxy Haro 11, revealing that merger-driven interactions displace HI gas, potentially facilitating the escape of ionizing radiation and contributing to cosmic reionization.

Contribution

It provides the first direct 21cm imaging of neutral gas in a nearby galaxy analog to reionization-era galaxies, linking gas displacement to LyC escape mechanisms.

Findings

Neutral gas offset by about 6 kpc from LyC sites

Merger interactions displace HI, aiding LyC escape

Galaxy interactions influence ionizing radiation escape

Abstract

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.