LAUSR

Ultraviolet light from early galaxies is thought to have ionized gas in the intergalactic medium. However, there are few observational constraints on this epoch because of the faintness of those galaxies and the redshift of their optical light into the infrared. We report the observation, in JWST imaging, of a distant galaxy that is magnified by gravitational lensing. JWST spectroscopy of the galaxy, at rest-frame optical wavelengths, detects strong nebular emission lines that are attributable to oxygen and hydrogen. The measured redshift is z = 9.51 ± 0.01, corresponding to 510 million years after the Big Bang. The galaxy has a radius of 16.2−7.2+4.6 parsecs, which is substantially more compact than galaxies with equivalent luminosity at z ~ 6 to 8, leading to a high star formation rate surface density. Description Editor’s summary The expansion of the Universe causes the light from distant galaxies to be redshifted to longer wavelengths. Candidate distant galaxies can be identified using imaging, but confirming their redshift requires spectroscopy. Williams et al. used near-infrared imaging and spectroscopy to identify a galaxy at redshift 9.5, corresponding to about 500 million years after the Big Bang. Little is known about galaxies at that early time. Emission lines in the spectrum allowed the authors to determine some of the galaxy’s physical properties, such as its abundance of elements heavier than helium, and they found that it is very compact and has a high density of star formation. —Keith T. Smith Spectroscopy of a compact galaxy at redshift 9.5 determines its physical properties only 500 million years after the Big Bang.