JWST Measurements of Neutral Hydrogen Fractions and Ionized Bubble Sizes at $z=7-12$ Obtained with Ly$\alpha$ Damping Wing Absorptions in 27 Bright Continuum Galaxies

Abstract

We present volume-averaged neutral hydrogen fractions $x_{\rm \HI}$ and ionized bubble radii $R_{\mathrm{b}}$ measured with Ly$\alpha$ damping wing absorption of galaxies at the epoch of reionization. We combine JWST/NIRSpec spectra taken by CEERS, GO-1433, DDT-2750, and JADES programs, and obtain a sample containing 27 bright UV-continuum ($M_{\mathrm{UV}}<-18.5\mathrm{mag}$) galaxies at $7<z<12$. We construct 4 composite spectra binned by redshift, and find the clear evolution of softening break towards high redshift at the rest-frame $1216$ Å, suggesting the increase of Ly$\alpha$ damping wing absorption. We estimate Ly$\alpha$ damping wing absorption in the galaxy spectra with realistic templates including Ly$\alpha$ emission and circum-galactic medium absorptions. Assuming the standard inside-out reionization picture having an ionized bubble with radius $R_b$ around a galaxy embedded in the intergalactic medium with $x_{\rm \HI}$, we obtain $x_{\rm \HI}$ ($R_{\mathrm{b}}$) values generally increasing (decreasing) from $x_{\rm \HI}={0.53}^{+0.18}_{-0.47}$ to ${0.92}_{-0.10}^{+0.08}$ ($\log R_{\mathrm{b}}={1.67}_{-0.16}^{+0.14}$ to ${-0.69}_{-0.24}^{+0.89}$ comoving Mpc) at redshift $7.12_{-0.08}^{+0.06}$ to $9.91_{-1.15}^{+1.49}$. The redshift evolution of $x_{\rm \HI}$ indicates a moderately late reionization history consistent with the one previously suggested from the electron scattering of cosmic microwave background and the evolution of UV luminosity function with an escape fraction $f_{\mathrm{esc}}\sim 0.2$. Our $R_{\mathrm{b}}$ measurements suggest that bubble sizes could be up to a few dex larger than the cosmic average values estimated by analytic calculations for a given $x_{\rm \HI}$, while our $R_{\mathrm{b}}$ measurements are roughly comparable with the values for merged ionized bubbles around bright galaxies predicted by recent numerical simulations.

Accepted for publication in ApJ. We have added discussion comparing fitting for low-resolution spectra and high resolution spectra. We also modified the inference method based on Bayesian theory

Cited by in corpus (5)

• Confirmation and refutation of very luminous galaxies in the early universe
• The THESAN project: connecting ionized bubble sizes to their local environments during the Epoch of Reionization
• Late-end reionization with ATON-HE: towards constraints from Lyman-$\alpha$ emitters observed with JWST
• The impact of faint AGN discovered by JWST on reionization
• The Lyman-limit photon mean free path at the end of late reionisation in the Sherwood-Relics simulations