Abstract

Lya damping wing absorption measurement is a useful tool to constrain the key cosmic reionization parameters including 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 Lya 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 27 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 Lya damping wing absorption in the galaxy spectra with a state-of-art stellar population synthesis model including Lya emission and host HI absorptions. Assuming the standard inside-out reionization picture having an ionized bubble with Rb around a galaxy in the intergalactic medium of xHI, we obtain xHI (Rb) values monotonically increasing (decreasing) trend from xHI = 0.54 to 0.95 (log Rb = 1.89 to -0.68 comoving Mpc) at redshift 7.12 to 9.91. We also estimate xHI at z 5.7 Subaru LAE catalog consists of 8182 galaxies, and we estimate xHI from Lya luminosity function and LAE clustering properties using a prediction based on semi-numerical simulation 21cmFAST. The redshift evolution of xHI between z=6 to 12 inferred from JWST and Subaru result indicate a very rapid reionization scenario progressing mainly at z=7-8.