Census of Ly$\alpha$ Emission from $\sim 600$ Galaxies at $z=5-14$: Evolution of the Ly$\alpha$ Luminosity Function and a Late Sharp Cosmic Reionization

TL;DR

This study analyzes Ly$ extalpha$ emission from approximately 600 high-redshift galaxies using JWST data, revealing a significant decline in Ly$ extalpha$ luminosity and a late, rapid reionization of the universe around redshift 6-7.

Contribution

First constraints on the Ly$ extalpha$ luminosity function at $z extasciimath 8-14$, showing a sharp increase in neutral hydrogen fraction and a late reionization epoch.

Findings

Ly$ extalpha$ galaxy fraction decreases with redshift.

Approximately 3 dex decline in Ly$ extalpha$ luminosity density from $z extasciimath 5$ to $z extasciimath 14$.

Reionization likely occurred rapidly around $z extasciimath 6-7$, with high neutral hydrogen fractions at higher redshifts.

Abstract

We present the statistical properties of Ly$\alpha$ emission in 586 galaxies at $z=4.5-14.2$, observed by multiple JWST/NIRSpec spectroscopy projects, including JADES, GLASS, CEERS, and GO/DDT programs. We obtain Ly$\alpha$ equivalent width (EW), Ly$\alpha$ escape fraction, and ionizing photon production efficiency measurements or upper limits for these galaxies, and confirm that the Ly$\alpha$ emitting galaxy fraction decreases towards higher redshifts. We derive Ly$\alpha$ luminosity functions from $z\sim 5$ to $z\sim 10-14$ with the observed Ly$\alpha$ EW distributions and galaxy UV luminosity functions, and find a $\sim3$ dex decrease in number density at $L_\mathrm{Ly\alpha}=10^{42}-10^{43}$ erg s$^{-1}$ over the redshift range. Notably, this study presents the first constraints on the Ly$\alpha$ luminosity function at $z\sim 8-14$. We obtain the neutral hydrogen fractions of $x_\mathrm{HI}=0.17_{-0.16}^{+0.23}$, $0.63_{-0.28}^{+0.18}$, $0.79_{-0.21}^{+0.13}$, and $0.88_{-0.13}^{+0.11}$ at $z\sim6$, $7$, $8-9$, and $10-14$, respectively, via comparisons of the reionization models developed by semi-numerical simulations with 21cmFAST explaining the observations of Ly$\alpha$, UV continuum, and Planck electron optical depth. The high $x_\mathrm{HI}$ values over $z\sim 7-14$ suggest a late and sharp reionization, with the primary reionization process occurring at $z\sim 6-7$. Such a late and sharp reionization is not easily explained by either a clumpy inter-galactic medium or sources of reionization in a classical faint-galaxy or a bright-galaxy/AGN scenario, unless a very high escape fraction or AGN duty cycle is assumed at $z\sim 6-7$.