Jades: The production and escape of ionizing photons from faint Lyman-alpha emitters in the epoch of reionization

Abstract

We present the properties of 17 faint Ly$\alpha$ emitting galaxies (LAEs) at $z>5.8$ from the JWST Advanced Deep Extragalactic Survey (JADES) in the Hubble Ultra Deep Field/GOODS-S. These LAEs span a redshift range $z\approx5.8-8.0$ and a UV magnitude range $M_{UV}\approx-17$ to $-20.6$, with the Ly$\alpha$ equivalent width (EW) in the range $\approx 25-350$ \AA. The detection of other rest-optical emission lines in the spectra of these LAEs enables the determination of accurate systemic redshifts and Ly{\alpha} velocity offsets, as well as the physical and chemical composition of their stars and interstellar media. These faint LAEs are consistent with metal-poor systems with high ionization parameters, similar to the general galaxy population at $z>6$. We measured an average ionizing photon production efficiency, log($\xi_\rm{ion}$/erg$^{-1}$ Hz) $\approx25.57$ across our LAEs, which does not evolve strongly with redshift. We report an anti-correlation between the Ly$\alpha$ escape fraction (f_\rm{esc}) and the velocity offset from systemic redshift, consistent with model expectations. We further find that the strength and velocity offset of Ly$\alpha$ are neither correlated with galaxy spectroscopic properties nor with $\xi_\rm{ion}$. We find a decrease in $f_\rm{esc}$(Ly$\alpha$) with redshift, indicative of decreasing sizes of ionized bubbles around LAEs at high redshifts. We used a range of galaxy properties to predict Lyman continuum $f_\rm{esc}$ for our LAEs, finding that the ionizing photon output into the intergalactic medium remains roughly constant across the observed Ly$\alpha$ EW, showing a mild increase at fainter M$_{UV}$ and at higher redshifts. We derived correlations between the ionizing photon output from LAEs and $M_{UV}$, Ly$\alpha$ EW and redshifts, which can be used to constrain the ionizing photon contribution of LAEs at $z > 6$ towards cosmic reionization.