The evolution of the metallicity gradient and the star formation
  efficiency in disc galaxies
  We study the oxygen abundance profiles of the gas-phase components in
hydrodynamical simulations of pre-prepared disc galaxies including major
mergers, close encounters and isolated configurations. We analyse the evolution
of the slope of oxygen abundance profiles and the specific star formation rate
(sSFR) along their evolution. We find that galaxy-galaxy interactions could
generate either positive and negative gas-phase oxygen profiles depending on
the state of evolution. Along the interaction, galaxies are found to have
metallicity gradients and sSFR consistent with observations, on average. Strong
gas inflows produced during galaxy-galaxy interactions or as a result of strong
local instabilities in gas-rich discs are able to produce both a quick dilution
of the central gas-phase metallicity and a sudden increase of the sSFR. Our
simulations show that, during these events, a correlation between the
metallicity gradients and the sSFR can be set up if strong gas inflows are
triggered in the central regions in short timescales. Simulated galaxies
without experiencing strong disturbances evolve smoothly without modifying the
metallicity gradients. Gas-rich systems show large dispersion along the
correlation. The dispersion in the observed relation could be interpreted as
produced by the combination of galaxies with different gas-richness and/or
experiencing different types of interactions. Hence, our findings suggest that
the observed relation might be the smoking gun of galaxies forming in a
hierarchical clustering scenario.
