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GALAXY EVOLUTION

Thirsty galaxies thriving on gas streams

Nature Astronomy volume 3, pages 796–797 (2019)Cite this article

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Young galaxies are most effective at converting gas into stars. Intense accretion of fuel is required to keep galaxies growing, but these gas streams have largely eluded observations. New instruments at optical telescopes are now uncovering clues of their existence.

In the first two to three billion years of cosmic history, galaxies are observed to undergo a very intense phase of growth. During this epoch, hundreds of stars are born every year within a typical active galaxy, compared with the handful of stars that are born in star-forming galaxies today. Hydrogen, the raw fuel for star formation, must be rapidly accreted from the surrounding intergalactic medium to sustain this powerful activity over time. Yet, despite the expectation that streams of infalling gas are common around galaxies, direct observations of gas accretion have remained scarce. Establishing how galaxies get their gas remains an open challenge for observational astrophysics, with simulations offering most of the information on how gas accretion might occur. In this issue of Nature Astronomy, D. Christopher Martin and colleagues1 provide additional clues to solve this conundrum. By using the Keck Cosmic Web Imager (KCWI) at the Keck Telescope, a new instrument designed specifically to image gas around galaxies, they have mapped in detail how hydrogen moves near two distant galaxies. With a novel modelling technique, these authors have uncovered new hints that the gas is moving towards the galaxies in flows that supply enough fuel to sustain the observed star formation activity.

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Fig. 1: Map of the projected gas density, colour-coded by temperature, of a simulated galaxy that is fed by cold-gas accretion at a redshift of z = 3.

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Authors and Affiliations

  1. Centre for Extragalactic Astronomy and Institute for Computational Cosmology, Durham University, Durham, UK

    Michele Fumagalli

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  1. Michele Fumagalli
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Correspondence to Michele Fumagalli.

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Fumagalli, M. Thirsty galaxies thriving on gas streams. Nat Astron 3, 796–797 (2019). https://doi.org/10.1038/s41550-019-0812-1

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