Can Blue UV-Bright Galaxies Drive Reionization at Cosmic Dawn? An M UV=-19.6 Galaxy with f esc about0.85 at z=9.244

We revisit EBG-1, a gravitationally lensed galaxy at z = 9.244, using newly obtained deep (14 hr) JWST/NIRSpec G235M (R about 1000) spectroscopy. EBG-1 is one of the bluest galaxies observed at z > 9. Along with its remarkably blue continuum of β= -2.99 plus or minus 0.15, we find very weak nebular emission from EBG-1. We obtain a 3σ upper limit of EW < 8.4 Angstrom for C III], a marginal H β measurement (EW = 256.2 plus or minus 122.2 Angstrom), and a 5σ detection of [O III] λ5007 (EW = 882.8 plus or minus 180.6 Angstrom). These lines suggest an oxygen abundance of 12 + (O/H) = 7.16 plus or minus 0.25 (3% Z) and (C/O) < -0.88 (3σ), placing EBG-1 on the C/O-metallicity sequence traced by lower-redshift galaxies. To constrain the escape fraction (f esc), we compare the observed UV slope and emission-line equivalent widths with synthetic spectra generated using BEAGLE. The models favor f esc 0.75, with f esc about 0.85 providing the best overall agreement with the observations. These results suggest that relatively UV-bright galaxies like EBG-1 can achieve the exceptionally high ionizing efficiencies supported by late reionization scenarios.