JADES: Primaeval Lyman-$\alpha$ emitting galaxies reveal early sites of reionisation out to redshift $z\sim 9$

$\text{require}mediawiki-texvc$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 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 ($M_{\text{UV}}\approx -20\mathrm{m}\mathrm{a}\mathrm{g}$) LAEs exhibit small Ly$\alpha$ velocity offsets from the systemic redshift, $\mathrm{\Delta }{v}_{\mathrm{L}\mathrm{y}\alpha }\lesssim 200\mathrm{k}\mathrm{m}{\mathrm{s}}^{-1}$, yet span a range of Ly$\alpha$ equivalent widths ($15\mathring{A}$, $31\mathring{A}$, and $132\mathring{A}$). The former two show moderate Ly$\alpha$ escape fractions ($f_{\mathrm{e}\mathrm{s}\mathrm{c},\mathrm{L}\mathrm{y}\alpha }\approx 10\mathrm{\%}$), whereas Ly$\alpha$ escapes remarkably efficiently from the third ($f_{\mathrm{e}\mathrm{s}\mathrm{c},\mathrm{L}\mathrm{y}\alpha }\approx 72\mathrm{\%}$), which moreover is very compact (half-light radius of $90\pm 10\mathrm{p}\mathrm{c}$). 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 $f_{\mathrm{e}\mathrm{s}\mathrm{c},\mathrm{L}\mathrm{y}\alpha }$, one of which reveals evidence for ionisation by an active galactic nucleus, may have reasonably produced small ionised 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 reionisation.