# Neutral ISM, Lyman-Alpha and Lyman-continuum in the nearby starburst Haro 11

## TL;DR

This study reanalyzes spectroscopic data of the local starburst galaxy Haro 11 to understand the mechanisms enabling Lyman Continuum escape, highlighting the role of a clumpy, partially transparent neutral medium influenced by star formation feedback.

## Contribution

It provides a detailed analysis of the neutral ISM properties in Haro 11, proposing a model of a clumpy, partially transparent medium facilitating LyC escape, which advances understanding of ionizing radiation leakage.

## Key findings

- Haro 11's ISM is likely a clumpy, neutral medium embedded in a highly ionized environment.
- Star formation feedback influences the creation of pathways for ionizing radiation.
- The galaxy's ISM model aligns with a partially transparent, optically thick medium to LyC escape.

## Abstract

Star forming galaxies are believed to be a major source of Lyman Continuum (LyC) radiation responsible for reionizing the early Universe. Direct observations of escaping ionizing radiation have however been few and with low escape fractions. In the local Universe, only ~10 emitters have been observed, with typical escape fractions of a few percent. The mechanisms regulating this escape need to be strongly evolving with redshift in order to account for the Epoch of Reionization. Gas content and star formation feedback are among the main suspects, known to both regulate neutral gas coverage and evolve with cosmic time. In this paper, we reanalyze HST-COS spectrocopy of the first detected local LyC leaker, Haro 11. We examine the connection between LyC leakage and Lyman-$\alpha$ line shape, and feedback-influenced neutral ISM properties like kinematics and gas distribution. We discuss the two extremes of an optically thin, density bounded ISM and a riddled, optically thick, ionization bounded ISM, and how Haro 11 fits into their theoretical predictions. We find that the most likely ISM model is a clumpy neutral medium embedded in a highly ionized medium with a combined covering fraction of unity and a residual neutral gas column density in the ionized medium high enough to be optically thick to Lyman-$\alpha$, but low enough to be at least partly transparent to Lyman continuum and undetected in Si II. This suggests that SF feedback and galaxy-scale interaction events play a major role in opening passageways for ionizing radiation through the neutral medium.