Gas inflows, star formation and metallicity evolution in galaxy pairs

TL;DR

This study uses simulations to explore how galaxy interactions cause gas inflows that dilute central metallicities and trigger star formation, and how subsequent star formation re-enriches the gas.

Contribution

It provides new insights into the timing and effects of gas inflows and star formation on metallicity evolution during galaxy interactions.

Findings

Gas inflows cause central metallicity dilution in galaxy pairs.

Star formation re-enriches the nuclear gas after dilution.

Timing of dilution and enrichment correlates with interaction stages.

Abstract

It has been known since many decades that galaxy interactions can induce star formation (hereafter SF) enhancements and that one of the driving mechanisms of this enhancement is related to gas inflows into the central galaxy regions, induced by asymmetries in the stellar component, like bars. In the last years many evidences have been accumulating, showing that interacting pairs have central gas-phase metallicities lower than those of field galaxies, by {\sim} 0.2-0.3 dex on average. These diluted ISM metallicities have been explained as the result of inflows of metal-poor gas from the outer disk to the galaxy central regions. A number of questions arises: What's the timing and the duration of this dilution? How and when does the SF induced by the gas inflow enrich the circumnuclear gas with re-processed material? Is there any correlation between the timing and strength of the dilution and the timing and intensity of the SF? By means of Tree-SPH simulations of galaxy major interactions, we have studied the effect that gas inflows have on the ISM dilution, and the effect that the induced SF has, subsequently, in re-enriching the nuclear gas. In this contribution, we present the main results of this study.