Abstract

Lyα damping wing absorption measurement is a useful tool to constrain the key cosmic reionization parameters including volume averaged neutral hydrogen fraction xHI, but the measurement had been limited only to the small number of extremely UV-continuum bright sources such as QSO/GRBs. For the first time, we constrain xHI and ionized bubble radii Rb by measuring Lyα damping wing absorptions using bright galaxy spectra detected in JWST observations. We combine JWST/NIRSpec spectra taken by CEERS, GO-1433, DDT-2750, and JADES programs, and obtain 26 bright (M_UV<-18.5) UV-continuum galaxies at 7 < z < 12. We construct 4 composite spectra binned by redshift and find the clear transition from sharp to soft spectral break towards high redshift at the restframe 1216 Å suggesting the increase of Lyα damping wing absorption. We estimate Lyα damping wing absorption in the galaxy spectra with a state-of-art stellar population synthesis model including Lyα emission and host HI absorptions. Assuming the standard inside-out reionization picture having an ionized bubble with Rb around a galaxy in the inter-galactic medium of xHI, we obtain xHI (Rb) values monotonically increasing (decreasing) trend from xHI = 0.54^{+0.13}_{−0.54} to {0.94}^{+0.06}_{−0.41} (log Rb = {1.89}^{+0.49}_{−1.54} to{−0.72}^{+1.57}_{−0.28} comoving Mpc) at redshift {7.122}^{+0.057}_{−0.077} to {10.28}^{+1.123}_{−1.404}. The redshift evolution of xHI indicates late reionization history consistent with the one suggested from the electron scattering of cosmic microwave background and the evolution of UV luminosity function with an escape fraction fesc∼ 0.2. Our Rb measurements are up to a few dex larger than the cosmic average values estimated by analytic calculations for a given xHI, while our Rb measurements are comparable with the values for merged ionized bubbles around bright galaxies predicted by recent numerical simulations.