JADES : primaeval Lyman α emitting galaxies reveal early sites of reionization out to redshift z ~ 9

Given the sensitivity of the resonant Lyman α (Ly α) transition to absorption by neutral hydrogen, observations of Ly α emitting galaxies (LAEs) have been widely used to probe the ionizing capabilities of reionization-era galaxies and their impact on the intergalactic medium (IGM). However, prior to JWST our understanding of the contribution of fainter sources and of ionized ‘bubbles’ at earlier stages of reionization remained uncertain. Here, we present the characterization of three exceptionally distant LAEs at z > 8, newly discovered by JWST/Near-Infrared Spectrograph in the JADES survey. These three similarly bright (MUV ≈ −20 mag) LAEs exhibit small Ly α velocity offsets from the systemic redshift, (Formula presented) 200 km s−1, yet span a range of Ly α equivalent widths (15, 31, and 132 Å). The former two show moderate Ly α escape fractions (fesc, Lyα ≈ 10 per cent), whereas Ly α escapes remarkably efficiently from the third (fesc, Lyα ≈ 72 per cent), which moreover is very compact (half-light radius of 90 ± 10 pc). We find these LAEs are low-mass galaxies dominated by very recent, vigorous bursts of star formation accompanied by strong nebular emission from metal-poor gas. We infer the two LAEs with modest fesc, Lyα, one of which reveals evidence for ionization by an active galactic nucleus, may have reasonably produced small ionized bubbles preventing complete IGM absorption of Ly α. The third, however, requires a ∼3 physical Mpc bubble, indicating faint galaxies have contributed significantly. The most distant LAEs thus continue to be powerful observational probes into the earlier stages of reionization.