LAUSR

Stars form in galaxies, from gas that has been accreted from the intergalactic medium. Simulations have shown that recycling of gas—the reaccretion of gas that was previously ejected from a galaxy—could sustain star formation in the early Universe. We observe the gas surrounding a massive galaxy at redshift 2.3 and detect emission lines from neutral hydrogen, helium, and ionized carbon that extend 100 kiloparsecs from the galaxy. The kinematics of this circumgalactic gas is consistent with an inspiraling stream. The carbon abundance indicates that the gas had already been enriched with elements heavier than helium, previously ejected from a galaxy. We interpret the results as evidence of gas recycling during high-redshift galaxy assembly. Description Editor’s summary Galaxies accrete gas from the surrounding intergalactic medium and then turn this gas into stars. Feedback processes such as supernova explosions enrich the gas with elements heavier than helium and can impart enough momentum to eject some gas out of the galaxy. S. Zhang et al. observed the intergalactic medium around a massive galaxy at redshift 2.3. In addition to emission lines caused by hydrogen and helium, they observed lines for carbon, indicating that the gas has been enriched with heavier elements. The kinematics are consistent with streams of gas spiraling toward the massive galaxy. The authors propose that the enriched gas has been recycled from an earlier period of star formation. —Keith T. Smith Streams of intergalactic gas enriched by previous star formation were observed spiraling toward a massive galaxy.