Misc,
Neutral ISM, Lyman-Alpha and Lyman-continuum in the nearby starburst Haro 11
(2017)cite arxiv:1701.08024Comment: 11 pages, 9 figures, 1 table. Accepted for publication in The Astrophysical Journal.
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.
