Galaxy And Mass Assembly (GAMA): the effect of close interactions on star formation in galaxies

TL;DR

This study investigates how galaxy interactions influence star formation, revealing that primary galaxies experience enhanced star formation while secondaries in minor mergers are suppressed, with effects varying on short timescales.

Contribution

It provides new insights into the differential impact of galaxy interactions on star formation based on galaxy mass and interaction phase, emphasizing short-term effects.

Findings

Star formation is enhanced in primary galaxies during interactions.

Secondary galaxies in minor mergers show suppressed star formation.

Short-term SFR indicators reveal recent interaction effects.

Abstract

The modification of star formation (SF) in galaxy interactions is a complex process, with SF observed to be both enhanced in major mergers and suppressed in minor pair interactions. Such changes likely to arise on short timescales and be directly related to the galaxy-galaxy interaction time. Here we investigate the link between dynamical phase and direct measures of SF on different timescales for pair galaxies, targeting numerous star-formation rate (SFR) indicators and comparing to pair separation, individual galaxy mass and pair mass ratio. We split our sample into the higher (primary) and lower (secondary) mass galaxies in each pair and find that SF is indeed enhanced in all primary galaxies but suppressed in secondaries of minor mergers. We find that changes in SF of primaries is consistent in both major and minor mergers, suggesting that SF in the more massive galaxy is agnostic to pair mass ratio. We also find that SF is enhanced/suppressed more strongly for short-time duration SFR indicators (e.g. H-alpha), highlighting recent changes to SF in these galaxies, which are likely to be induced by the interaction. We propose a scenario where the lower mass galaxy has its SF suppressed by gas heating or stripping, while the higher mass galaxy has its SF enhanced, potentially by tidal gas turbulence and shocks. This is consistent with the seemingly contradictory observations for both SF suppression and enhancement in close pairs.