Date: 12/15/2024
Harvard ADS: JADES: primaeval Lyman α emitting galaxies reveal early sites of reionization out to redshift z ~ 9
Paper 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} ~ -20 \, \mathrm{mag}) LAEs exhibit small Ly \alpha velocity offsets from the systemic redshift, \Delta v_\rm{{Ly\alpha }} <~ 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 }} ~ 10~{{\rm per\,cent}}), whereas Ly \alpha escapes remarkably efficiently from the third (f_\rm{esc, {Ly\alpha }} ~ 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 ~ \!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.
