Gas inflow and metallicity drops in star-forming galaxies
  Gas inflow feeds galaxies with low metallicity gas from the cosmic web,
sustaining star formation across the Hubble time. We make a connection between
these inflows and metallicity inhomogeneities in star-forming galaxies, by
using synthetic narrow-band images of the Halpha emission line from zoom-in AMR
cosmological simulations of galaxies with stellar masses of $M \simeq 10^9
$Msun at redshifts z=2-7. In $\sim$50\% of the cases at redshifts lower than 4,
the gas inflow gives rise to star-forming, Halpha-bright, off-centre clumps.
Most of these clumps have gas metallicities, weighted by Halpha luminosity,
lower than the metallicity in the surrounding interstellar medium by $\sim$0.3
dex, consistent with observations of chemical inhomogeneities at high and low
redshifts. Due to metal mixing by shear and turbulence, these metallicity drops
are dissolved in a few disc dynamical times. Therefore, they can be considered
as evidence for rapid gas accretion coming from cosmological inflow of pristine
gas.
