The mass-metallicity relation of tidal dwarf galaxies
  Dwarf galaxies generally follow a mass-metallicity (MZ) relation, where more
massive objects retain a larger fraction of heavy elements. Young tidal dwarf
galaxies (TDGs), born in the tidal tails produced by interacting gas-rich
galaxies, have been thought to not follow the MZ relation, because they inherit
the metallicity of the more massive parent galaxies. We present chemical
evolution models to investigate if TDGs that formed at very high redshifts,
where the metallicity of their parent galaxy was very low, can produce the
observed MZ relation. Assuming that galaxy interactions were more frequent in
the denser high-redshift universe, TDGs could constitute an important
contribution to the dwarf galaxy population. The survey of chemical evolution
models of TDGs presented here captures for the first time an initial mass
function (IMF) of stars that is dependent on both the star formation rate and
the gas metallicity via the integrated galactic IMF (IGIMF) theory. As TDGs
form in the tidal debris of interacting galaxies, the pre-enrichment of the
gas, an underlying pre-existing stellar population, infall, and mass dependent
outflows are considered. The models of young TDGs that are created in strongly
pre-enriched tidal arms with a pre-existing stellar population can explain the
measured abundance ratios of observed TDGs. The same chemical evolution models
for TDGs, that form out of gas with initially very low metallicity, naturally
build up the observed MZ relation. The modelled chemical composition of ancient
TDGs is therefore consistent with the observed MZ relation of satellite
galaxies.
