Gas inflow and metallicity drops in star-forming galaxies

TL;DR

This study links gas inflow from the cosmic web to metallicity inhomogeneities in star-forming galaxies, showing that low-metallicity gas inflows create transient, off-center, low-metallicity star-forming clumps observable in simulations.

Contribution

It demonstrates, through cosmological simulations, that gas inflows produce observable metallicity drops and inhomogeneities in star-forming galaxies, providing evidence for rapid accretion of pristine gas.

Findings

Gas inflows create off-center, low-metallicity star-forming clumps.

Metallicity drops are transient, dissolving within a few dynamical times.

Simulations match observed chemical inhomogeneities at various redshifts.

Abstract

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.