James Webb Space Telescope Feed Post

Date: 6/10/2024

Harvard ADS: Lyα emission in galaxies at z ≃ 5-6: new insight from JWST into the statistical distributions of Lyα properties at the end of reionization

Paper abstract: JWST has recently sparked a new era of Lya spectroscopy, delivering the first measurements of the Lya 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 Lya 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 Lya velocity offsets, escape fractions, and EWs in z ? 5-6 galaxies. We find that galaxies with large Lya 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 Lya 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 Lya 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 Lya emission near line centre. This effect will make it challenging to use Lya peak offsets as a probe of Lyman continuum leakage at z ? 5-6. We use our z ? 5-6 Lya distributions to make predictions for typical Lya properties at z ? 8 and discuss implications of a recently discovered Lya emitter at z ? 8.5 with a small peak velocity offset (156 km s-1).