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Arxiv: Lyα emission in galaxies at z\simeq5-6: new insight from JWST into the statistical distributions of Lyα properties at the end of reionization Published: 2/8/2024 11:42:15 PM Updated: 2/8/2024 11:42:15 PM

Paper abstract: JWST has recently sparked a new era of Lya spectroscopy, delivering the firstmeasurements of the Lya escape fraction and velocity profile in typicalgalaxies at z~6-10. These observations offer new prospects for insight into theearliest stages of reionization. But to realize this potential, we need robustintrinsic models of Lya properties in galaxies at z~5-6 when the IGM is mostlyionized. Here we use new JWST observations from the JADES and FRESCO surveys tocharacterize statistical distributions of Lya velocity offsets, escapefractions, and EWs in z~5-6 galaxies that will be applicable to growingdatasets at z>6. We find that galaxies with large Lya escape fractions (>0.2)are common at z~5-6, comprising 30% of Lyman break selected samples. Comparingto literature studies, our census suggests that Lya becomes more prevalent inthe galaxy population toward higher redshift from z~3 to z~6, although we findthat this evolution slows considerably between z~5 and z~6, consistent withmodest attenuation from residual HI in the mostly ionized IGM at z~5-6. We findsignificant evolution in Lya velocity profiles between z~2-3 and z~5-6. Atlower redshifts, the strongest Lya emitters often have line profiles peakingnear the systemic redshift, reflecting escape through low HI density channels.At z~5-6, the strongest Lya emitters have profiles with flux emerging attypical redshifted velocities ~230km/s. The rarity of Lya emitters with peakflux near the systemic redshift at z~5-6 may reflect the influence of resonantscattering from residual HI in the IGM. This effect will make it challenging touse Lya peak offsets as a probe of Lyman continuum leakage at z~5-6. We use ourz~5-6 Lya distributions to make predictions for typical Lya properties at z>8and discuss implications of a recently-discovered Lya emitter at z=8.5 with asmall peak velocity offset (156km/s).