JADES: Primeval Lyman-α emitting galaxies reveal early sites of reionisation out to redshift z ∼ 9

mediawiki-texvcGiven the sensitivity of the resonant Lyman-α (Lyα) transition to absorption by neutral hydrogen, observations of Lyα emitting galaxies (LAEs) have been widely used to probe the ionising capabilities of reionisation-era galaxies and their impact on the intergalactic medium (IGM). However, prior to JWST our understanding of the contribution of fainter sources and of ionised `bubbles' at earlier stages of reionisation remained uncertain. Here, we present the characterisation of three exceptionally distant LAEs at z>8, newly discovered by JWST/NIRSpec in the JADES survey. These three similarly bright (M_UV≈ -20 mag) LAEs exhibit small Lyα velocity offsets from the systemic redshift, Δ v_Lyα≲ 200 km s^-1, yet span a range of Lyα equivalent widths (15 Å, 31 Å, and 132 Å). The former two show moderate Lyα escape fractions (f_esc,Lyα≈ 10%), whereas Lyα escapes remarkably efficiently from the third (f_esc,Lyα≈ 71%), 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 f_esc,Lyα, one of which reveals evidence for ionisation by an active galactic nucleus, may have reasonably produced small ionised bubbles preventing complete IGM absorption of Lyα. 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 reionisation.