Observational studies have revealed that galaxy pairs tend to have lower
gas-phase metallicity than isolated galaxies. This metallicity deficiency can
be caused by inflows of low-metallicity gas due to the tidal forces and
gravitational torques associated with galaxy mergers, diluting the metal
content of the central region. In this work we demonstrate that such
metallicity dilution occurs in state-of-the-art cosmological simulations of
galaxy formation. We find that the dilution is typically 0.1 dex for major
mergers, and is noticeable at projected separations smaller than 40 kpc. For
minor mergers the metallicity dilution is still present, even though the
amplitude is significantly smaller. Consistent with previous analysis of
observed galaxies we find that mergers are outliers from the \emph{fundamental
metallicity relation}, with deviations being larger than expected for a
Gaussian distribution of residuals. Our large sample of mergers within full
cosmological simulations also makes it possible to estimate how the star
formation rate enhancement and gas consumption timescale behave as a function
of the merger mass ratio. We confirm that strong starbursts are likely to occur
in major mergers, but they can also arise in minor mergers if more than two
galaxies are participating in the interaction, a scenario that has largely been
ignored in previous work based on idealised isolated merger simulations.Comment: Submitted to MNRA