Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Joris Witstok, Peter Jakobsen, Roberto Maiolino, Jakob M. Helton, Benjamin D. Johnson
| Summary:
$require{mediawiki-texvc}$Cosmic Reionisation commenced when ultraviolet
(UV) radiation produced in the first galaxies began illuminating the cold,
neutral gas that filled the primordial Universe. Recent James Webb Space
Telescope (JWST) observations have shown that surprisingly UV-bright galaxies
were in place beyond redshift $z = 14$, when the Universe was less than $300 ,
mathrm{Myr}$ old. Smooth turnovers of their UV continua have been interpreted
as damping-wing absorption of Lyman-$alpha$ (Ly$alpha$), the principal
hydrogen transition. However, spectral signatures encoding crucial properties
of these sources, such as their emergent radiation field, largely remain
elusive. Here we report spectroscopy from the JWST Advanced Deep Extragalactic
Survey (JADES) of a galaxy at redshift $z = 13.0$ that reveal a singular,
bright emission line unambiguously identified as Ly$alpha$, in addition to a
smooth turnover. We observe an equivalent width of $text{EW}_mathrm{Lyalpha}
> 40 , AA$ (rest frame), previously only seen at $z < 9$ where the
intervening intergalactic medium (IGM) becomes increasingly ionised. Together
with an extremely blue UV continuum, the unexpected Ly$alpha$ emission
indicates the galaxy is a prolific producer and leaker of ionising photons.
This suggests massive, hot stars or an active galactic nucleus (AGN) have
created an early reionised region to prevent complete extinction of Ly$alpha$,
thus shedding new light on the nature of the earliest galaxies and the onset of
Reionisation only $330 , mathrm{Myr}$ after the Big Bang.
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