Kavli Affiliate: Debora Sijacki
| First 5 Authors: Callum Witten, Nicolas Laporte, Sergio Martin-Alvarez, Debora Sijacki, Yuxuan Yuan
| Summary:
A major event in cosmic history is the genesis of the first starlight in our
Universe, ending the ”Dark Ages”. During this epoch, the earliest luminous
sources were enshrouded in neutral and pristine gas, which was gradually
ionised in a process called ”reionisation”. Hence, one of the brightest
emission lines in star-forming galaxies, Lyman-$alpha$ (Ly-$alpha$), was
predicted to emerge only towards the end of the epoch of reionisation, about
one billion years after the Big Bang. However, this picture has been challenged
over the past decade by the surprising detection of Ly-$alpha$ in galaxies
less than 500 million years old. Here we show, by taking advantage of both
high-resolution and high-sensitivity images from the James Webb Space Telescope
programs PRIMER, CEERS and FRESCO, that all galaxies in our sample of
Ly-$alpha$ emitters deep in the epoch of reionisation have close companions.
To understand the physical processes that lead to the observed Ly-$alpha$
emission in our sample, we take advantage of novel on-the-fly radiative
transfer magnetohydrodynamical simulations with cosmic ray feedback. We find
that in the early Universe, the rapid build up of mass through frequent
galactic mergers leads to very bursty star formation which in turn drives
episodes of high intrinsic Ly-$alpha$ emission and facilitates the escape of
Ly-$alpha$ photons along channels cleared of neutral gas. These merging
galaxies reside in clustered environments thus creating sufficiently large
ionised bubbles. This presents a solution to the long-standing puzzle of the
detection of Ly-$alpha$ emission deep into the epoch of reionisation.
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