Kavli Affiliate: Michael D. Gladders
| First 5 Authors: Keunho J. Kim, Matthew B. Bayliss, Jane R. Rigby, Michael D. Gladders, John Chisholm
| Summary:
Extreme, young stellar populations are considered the primary contributor to
cosmic re-ionization. How Lyman-continuum (LyC) escapes these galaxies remains
highly elusive, and it is challenging to observe this process in actual LyC
emitters without resolving the relevant physical scales. We investigate the
Sunburst Arc: a strongly lensed, LyC emitter at $z =2.37$ that reveals an
exceptionally small scale (tens of parsecs) region of high LyC escape. The
small ($<$ 100 pc) LyC leaking region has extreme properties: a very blue UV
slope ($beta = -2.9 pm 0.1$), high ionization state ([O III]$lambda 5007$/[O
II]$lambda 3727 $ $= 11 pm 3$ and [O III]$lambda 5007$/H$beta$ $=6.8 pm
0.4$), strong oxygen emission (EW([O III]) $= 1095 pm 40 r{A}$), and high
Lyman-$alpha$ escape fraction ($0.3 pm 0.03$), none of which are found in
non-leaking regions of the galaxy. The leaking region’s UV slope is consistent
with approximately “pure” stellar light that is minimally contaminated by
surrounding nebular continuum emission or extinguished by dust. These results
suggest a highly anisotropic LyC escape process such that LyC is produced and
escapes from a small, extreme starburst region where the stellar feedback from
an ionizing star cluster creates one or more “pencil beam” channels in the
surrounding gas through which LyC can directly escape. Such anisotropic escape
processes imply that random sightline effects drive the significant scatters
between measurements of galaxy properties and LyC escape fraction, and that
strong lensing is a critical tool for resolving the processes that regulate the
ionizing budget of galaxies for re-ionization.
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