Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Joris Witstok, Roberto Maiolino, Renske Smit, Gareth C. Jones, Andrew J. Bunker
| Summary:
$require{mediawiki-texvc}$Given the sensitivity of the resonant
Lyman-$mathrm{alpha}$ (Ly$mathrm{alpha}$) transition to absorption by
neutral hydrogen, observations of Ly$mathrm{alpha}$ 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 ($M_text{UV} approx -20,mathrm{mag}$) LAEs exhibit small
Ly$mathrm{alpha}$ velocity offsets from the systemic redshift, $Delta
v_mathrm{Lyalpha} lesssim 200,mathrm{km,s^{-1}}$, yet span a range of
Ly$mathrm{alpha}$ equivalent widths ($15,AA$, $31,AA$, and $132,AA$).
The former two show moderate Ly$mathrm{alpha}$ escape fractions
($f_mathrm{esc,Lyalpha} approx 10%$), whereas Ly$mathrm{alpha}$ escapes
remarkably efficiently from the third ($f_mathrm{esc,Lyalpha} approx 72%$),
which moreover is very compact (half-light radius of $90pm10,mathrm{pc}$).
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 $f_mathrm{esc,Lyalpha}$, 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$mathrm{alpha}$. 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.
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