The mass-metallicity relation of tidal dwarf galaxies

TL;DR

This paper uses advanced chemical evolution models to demonstrate that tidal dwarf galaxies, especially those formed early in the universe, can naturally develop a mass-metallicity relation consistent with observations, challenging previous assumptions.

Contribution

It introduces the first chemical evolution models of TDGs incorporating an IMF dependent on SFR and metallicity, explaining their observed MZ relation.

Findings

Models of pre-enriched TDGs match observed abundance ratios.

Low-metallicity TDGs naturally develop the MZ relation.

Ancient TDGs' composition aligns with satellite galaxy observations.

Abstract

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.