Galaxy mergers and the mass-metallicity relation: Evidence for nuclear metal dilution and flattened gradients from numerical simulations

Abstract

Recent results comparing interacting galaxies to the mass-metallicity relation show that their nuclear oxygen abundances are unexpectedly low. We present analysis of N-body/smoothed-particle hydrodynamics numerical simulations of equal-mass mergers that confirm the hypothesis that these underabundances are accounted for by radial inflow of low-metallicity gas from the outskirts of the two merging galaxies. The underabundances arise between first and second pericenters, and the simulated abundance dilution is in good agreement with observations. The simulations further predict that the radial metallicity gradients of the disk galaxies flatten shortly after first passage, due to radial mixing of gas. These predictions will be tested by future observations of the radial metallicity distributions in interacting galaxies.