Properties of Molecular Gas in Galaxies in Early and Mid Stages of Interaction. III. Resolved Kennicutt-Schmidt Law

TL;DR

This study examines how galaxy interactions affect star formation and molecular gas properties, finding that early-stage interactions do not significantly alter the Kennicutt-Schmidt law or dense gas content, but can locally enhance star formation efficiency.

Contribution

It provides detailed analysis of star formation laws and efficiency at both galaxy and kpc scales during early and mid stages of galaxy interactions, highlighting local variations and the stability of the Kennicutt-Schmidt law.

Findings

Galaxy-scale SFR remains within a factor of three of isolated galaxies.

Local SFE is asymmetrically enhanced, possibly due to shocks.

Kennicutt-Schmidt law index is consistent with isolated galaxies in early stages.

Abstract

We study properties of the interstellar medium, an ingredient of stars, and star formation activity, in four nearby galaxy pairs in the early and mid stages of interaction for both a galaxy scale and a kpc scale. The galaxy-scale Kennicutt-Schmidt law shows that seven of eight interacting galaxies have a star formation rate within a factor of three compared with the best-fit of the isolated galaxies, although we have shown that molecular hydrogen gas is efficiently produced from atomic hydrogen during the interaction in the previous paper. The galaxy-scale specific star formation rate (sSFR) and star formation efficiency (SFE) in interacting galaxies are comparable to those in isolated galaxies. We also investigate SFE and the Kennicutt-Schmidt law on a kpc scale. The spatial distributions of SFE reveal that SFE is locally enhanced, and the enhanced regions take place asymmetrically or at off-centre regions. The local enhancement of SFE could be induced by shock. We find that the index of the Kennicutt-Schmidt law for the interacting galaxies in the early stage is 1.30$\pm$0.04, which is consistent with that of the isolated galaxies. Since CO emission, which is used in the Kennicutt-Schmidt law, is a tracer of the amount of molecular gas, this fact suggests that dense gas, which is more directly connected to star formation, is not changed at the early stage of interaction.