Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Mengtao Tang, Daniel P. Stark, Richard S. Ellis, Fengwu Sun, Michael Topping
| Summary:
JWST has recently sparked a new era of Ly$alpha$ spectroscopy, delivering
the first measurements of the Ly$alpha$ escape fraction and velocity profile
in typical galaxies at $zsimeq6-10$. These observations offer new prospects
for insight into the earliest stages of reionization. But to realize this
potential, we need robust models of Ly$alpha$ properties in galaxies at
$zsimeq5-6$ when the IGM is mostly ionized. Here we use new JWST observations
from the JADES and FRESCO surveys combined with VLT/MUSE and Keck/DEIMOS data
to characterize statistical distributions of Ly$alpha$ velocity offsets,
escape fractions, and EWs in $zsimeq5-6$ galaxies. We find that galaxies with
large Ly$alpha$ escape fractions (> 0.2) are common at $zsimeq5-6$,
comprising 30 per cent of Lyman break selected samples. Comparing to literature
studies, our census suggests that Ly$alpha$ becomes more prevalent in the
galaxy population toward higher redshift from $zsim3$ to $zsim6$, although we
find that this evolution slows considerably between $zsim5$ and $zsim6$,
consistent with modest attenuation from residual HI in the mostly ionized IGM
at $zsimeq5-6$. We find significant evolution in Ly$alpha$ velocity profiles
between $zsimeq2-3$ and $zsimeq5-6$, likely reflecting the influence of
resonant scattering from residual intergalactic HI on the escape of Ly$alpha$
emission near line center. This effect will make it challenging to use
Ly$alpha$ peak offsets as a probe of Lyman continuum leakage at $zsimeq5-6$.
We use our $zsimeq5-6$ Ly$alpha$ distributions to make predictions for
typical Ly$alpha$ properties at $zgtrsim8$ and discuss implications of a
recently-discovered Ly$alpha$ emitter at $zsimeq8.5$ with a small peak
velocity offset (156 km s$^{-1}$).
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