Lyα emission in galaxies at z ≃ 5-6: new insight from JWST into the statistical distributions of Lyα properties at the end of reionization
Charlot, Stéphane; Chevallard, Jacopo; Maseda, Michael V.; Arribas, Santiago; Bunker, Andrew J.; Maiolino, Roberto; Jones, Gareth C.; Kumari, Nimisha; Willott, Chris; Chen, Zuyi; Tang, Mengtao; Stark, Daniel P.; Ellis, Richard S.; Lyu, Jianwei; Saxena, Aayush; Witstok, Joris; Sun, Fengwu; Tacchella, Sandro; Williams, Christina C.; Baker, William M.; Bhatawdekar, Rachana; Boyett, Kristan; Whitler, Lily; Robertson, Brant; Topping, Michael
United States, United Kingdom, Spain, Australia, France, Canada
Abstract
JWST has recently sparked a new era of Lyα spectroscopy, delivering the first measurements of the Lyα escape fraction and velocity profile in typical galaxies at z ≃ 6-10. These observations offer new prospects for insight into the earliest stages of reionization. But to realize this potential, we need robust models of Lyα properties in galaxies at z ≃ 5-6 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 Lyα velocity offsets, escape fractions, and EWs in z ≃ 5-6 galaxies. We find that galaxies with large Lyα escape fractions (>0.2) are common at z ≃ 5-6, comprising 30 per cent of Lyman break selected samples. Comparing to literature studies, our census suggests that Lyα becomes more prevalent in the galaxy population towards higher redshift from z ~ 3 to z ~ 6, although we find that this evolution slows considerably between z ~ 5 and z ~ 6, consistent with modest attenuation from residual H I in the mostly ionized IGM at z ≃ 5-6. We find significant evolution in Lyα velocity profiles between z ≃ 2-3 and z ≃ 5-6, likely reflecting the influence of resonant scattering from residual intergalactic H I on the escape of Lyα emission near line centre. This effect will make it challenging to use Lyα peak offsets as a probe of Lyman continuum leakage at z ≃ 5-6. We use our z ≃ 5-6 Lyα distributions to make predictions for typical Lyα properties at z ≳ 8 and discuss implications of a recently discovered Lyα emitter at z ≃ 8.5 with a small peak velocity offset (156 km s-1).