2024ApJ...971..124U

We present volume-averaged neutral hydrogen fractions x_H I_ and ionized bubble radii R_b measured with Lyα damping wing absorption of galaxies at the epoch of reionization. We combine JWST/NIRSpec spectra taken by the CEERS, GO-1433, DDT-2750, and JADES programs and obtain a sample containing 27 bright UV-continuum (M_UV < -18.5 mag) galaxies at 7 < z < 12. We construct four composite spectra binned by redshift and find the clear evolution of the softening break toward high redshift at rest-frame 1216 Å, suggesting an increase of Lyα damping wing absorption. We estimate Lyα damping wing absorption in the galaxy spectra with realistic templates including Lyα emission and circumgalactic 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_H I_, we obtain x_H I_ (R_b) values generally increasing (decreasing) from ${x}_{{\rm{H}}\,{\rm\small{I}}}={0.53}_{-0.47}^{+0.18}$ to ${0.92}_{-0.10}^{+0.08}$ ($\mathrm{log}{R}_{b}={1.67}_{-0.16}^{+0.14}$ 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_H I_ 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_esc ∼ 0.2. Our R_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_H I_, while our R_b measurements are roughly comparable with the values for merged ionized bubbles around bright galaxies predicted by recent numerical simulations.