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

ABSTRACT Given the sensitivity of the resonant Lyman $\alpha$ (Ly $\alpha $) transition to absorption by neutral hydrogen, observations of Ly $\alpha$ 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 $z \gt 8$, newly discovered by JWST/Near-Infrared Spectrograph in the JADES survey. These three similarly bright ($M_\text{UV} \approx -20 \, \mathrm{mag}$) LAEs exhibit small Ly $\alpha$ velocity offsets from the systemic redshift, $\Delta v_\rm{{Ly\alpha }} \lesssim 200 \, \mathrm{km \, s^{-1}}$, yet span a range of Ly $\alpha$ equivalent widths (15, 31, and $132 \, \mathring{\rm A}$). The former two show moderate Ly $\alpha$ escape fractions ($f_\rm{esc, {Ly\alpha }} \approx 10~{{\rm per\,cent}}$), whereas Ly $\alpha$ escapes remarkably efficiently from the third ($f_\rm{esc, {Ly\alpha }} \approx 72~{{\rm per\,cent}}$), which moreover is very compact (half-light radius of $90 \pm 10 \, \mathrm{pc}$). 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 $f_\rm{esc, {Ly\alpha }}$, 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 $\alpha$. The third, however, requires a $\sim \!3 \, \text{physical Mpc}$ bubble, indicating faint galaxies have contributed significantly. The most distant LAEs thus continue to be powerful observational probes into the earlier stages of reionization.