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

2024; Oxford University Press; Volume: 531; Issue: 2 Linguagem: Inglês

10.1093/mnras/stae1338

1365-2966

Mengtao Tang, Daniel P. Stark, Richard S. Ellis, Fengwu Sun, Michael W. Topping, Brant Robertson, Sandro Tacchella, S. Arribas, William Baker, Rachana Bhatawdekar, Kristan Boyett, Andrew J. Bunker, S. Charlot, Zuyi Chen, Jacopo Chevallard, Gareth C. Jones, Nimisha Kumari, Jianwei Lyu, R. Maiolino, Michael V. Maseda, Aayush Saxena, Lily Whitler, Christina C. Williams, Chris J. Willott, Joris Witstok,

Cosmology and Gravitation Theories

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).