Gas-Phase Oxygen Gradients in Strongly Interacting Galaxies: I. Early-Stage Interactions

TL;DR

This study shows that strongly interacting galaxies experience nuclear metal dilution and flattened metallicity gradients due to gas inflow, with observations closely matching simulation predictions, confirming the impact of interactions on galaxy chemical composition.

Contribution

The paper provides the first extensive observational evidence linking galaxy interactions to metallicity gradient flattening and nuclear dilution, validating simulation models.

Findings

Interacting galaxies have about half the metallicity gradients of isolated galaxies.

Observed gradients and nuclear metallicities match simulation predictions.

Strong interactions cause gas inflow leading to metallicity dilution.

Abstract

A consensus is emerging that interacting galaxies show depressed nuclear gas metallicities compared to isolated star-forming galaxies. Simulations suggest that this nuclear underabundance is caused by interaction-induced inflow of metal-poor gas, and that this inflow concurrently flattens the radial metallicity gradients in strongly interacting galaxies. We present metallicities of over 300 HII regions in a sample of 16 spirals that are members of strongly interacting galaxy pairs with mass ratio near unity. The deprojected radial gradients in these galaxies are about half of those in a control sample of isolated, late-type spirals. Detailed comparison of the gradients with simulations show remarkable agreement in gradient distributions, the relationship between gradients and nuclear underabundances, and the shape of profile deviations from a straight line. Taken together, this evidence conclusively demonstrates that strongly interacting galaxies at the present day undergo nuclear metal dilution due to gas inflow, as well as significant flattening of their gas-phase metallicity gradients, and that current simulations can robustly reproduce this behavior at a statistical level.