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Gas accretion as the origin of chemical abundance gradients in distant galaxies


It has recently been suggested1,2 that galaxies in the early Universe could have grown through the accretion of cold gas, and that this may have been the main driver of star formation and stellar mass growth3,4,5. Because the cold gas is essentially primordial, it has a very low abundance of elements heavier than helium (referred to as metallicity). If funnelled to the centre of a galaxy, it will result in the central gas having an overall lower metallicity than gas further from the centre, because the gas further out has been enriched by supernovae and stellar winds, and not diluted by the primordial gas. Here we report chemical abundances across three rotationally supported star-forming galaxies at redshift z ≈ 3, only 2 Gyr after the Big Bang. We find ‘inverse’ gradients, with the central, star-forming regions having lower metallicities than less active ones, which is opposite to what is seen in local galaxies6,7. We conclude that the central gas has been diluted by the accretion of primordial gas, as predicted by ‘cold flow’ models.

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Figure 1: Surface brightness and velocity of the [O  iii ] 5,007 Å line, and metallicity maps.
Figure 2: Gas fractions for the different regions in the observed galaxies.


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SINFONI data were obtained from observations made with the ESO Telescopes at the Paranal Observatories. We thank the ESO staff for their work and support. This work was supported by INAF and ASI.

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All authors have contributed extensively to data reduction and interpretation.

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Correspondence to G. Cresci.

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Cresci, G., Mannucci, F., Maiolino, R. et al. Gas accretion as the origin of chemical abundance gradients in distant galaxies. Nature 467, 811–813 (2010).

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