Massive Galaxy Fed by Cold Cosmic Carbon Stream

Radio telescope observations have revealed a cold stream of intergalactic atomic carbon gas feeding star formation in a massive radio galaxy in the young Universe. The findings provide observational evidence supporting theoretical cosmological models and offer new insights into the origins of the cosmic materials that enable galaxy and star formation. Galaxies grow and evolve by accreting gas, either in mergers with other galaxies or from streams of cold molecular gas that thread through the intergalactic medium. Simulations suggest that this latter type of accretion, also known as cold stream accretion, may be a key mechanism driving the observed high star formation rates and rapid development of galaxies early in the history of the Universe. However, the physics underlying cold accretion streams are not well understood and, due to their elusive nature, it has been challenging to observe and confirm the existence of such streams feeding massive galaxies. Using the Atacama Large Millimeter/submillimeter Array (ALMA), Bjorn Emonts and colleagues mapped the atomic carbon gas surrounding the galaxy 4C 41.17 – a massive radio galaxy in the early Universe at redshift 3.8. To maximize the radio telescopes surface brightness sensitivity, Emonts et al. used ALMA's most compact and low-resolution configuration, which likely helped them detect a cold molecular stream where past studies haven't, the authors say. The submillimeter observations revealed a narrow stream of cold gas extending at least 100 kiloparsecs (~326,000 lightyears) outside the galaxy and into the intergalactic medium – a distance several times larger than the galaxy it appears to be feeding. According to the authors, the observations are consistent with cold gas streams predicted by cosmological models, and the mass of the cold atomic gas being funneled into the massive galaxy could fuel star formation for more than 500 million years. "Having observations that match well to previous predictions from simulations has been long in the making," writes Caitlin Casey in a related Perspective. "Further observations of cold streams that span a broad range of galaxies are needed to determine the processes that feed gas into galaxies."