LAUSR

The growth of galaxies in the early Universe is driven by accretion of circum- and intergalactic gas. Simulations have predicted that steady streams of cold gas penetrate the dark matter halos of galaxies and provide the raw material necessary to sustain star formation. We report a filamentary stream of gas that extends for 100 kiloparsecs and connects to the massive radio galaxy 4C 41.17. We detected the stream using submillimeter observations of the 3P1 to 3P0 emission from the [C i] line of atomic carbon, a tracer of neutral atomic or molecular hydrogen gas. The galaxy contains a central gas reservoir that is fueling a vigorous starburst. Our results show that the raw material for star formation can be present in cosmic streams outside galaxies. Description An intergalactic gas stream at cosmic noon Galaxies grow by accreting material, either in mergers with other galaxies or from gas in the intergalactic medium. Emonts et al. used submillimeter observations to map the atomic carbon gas around a massive galaxy at redshift 3.8, early in a period known as cosmic noon, when galaxies were rapidly assembling (see the Perspective by Casey). They identified a stream of cold gas several times the size of the galaxy extending away from it into the intergalactic medium. The mass of gas in the stream would be sufficient to maintain star formation in the galaxy for hundreds of millions of years if it is accreted. —KTS Submillimeter observations show a cold stream of intergalactic gas connecting to a massive galaxy at redshift 3.8.