Gas flows in galaxies: the relative importance of mergers and bars

TL;DR

This study compares the effectiveness of galaxy mergers and bars in driving gas inflows, finding that bars trigger at least three times more central star formation than interactions, despite both processes enhancing star formation.

Contribution

It provides a direct comparison of gas inflow efficiency from mergers and bars using SDSS data, highlighting the dominant role of bars in star formation.

Findings

Bars are more effective in triggering central star formation than galaxy interactions.

Galaxy pairs show suppressed metallicity, while barred galaxies are metal-rich for their mass.

Bars enhance star formation primarily in galaxies with stellar mass >10^10 M_solar.

Abstract

Galaxy-galaxy interactions and large scale galaxy bars are usually considered as the two main mechanisms for driving gas to the centres of galaxies. By using large samples of galaxy pairs and visually classified bars from the Sloan Digital Sky Survey (SDSS), we compare the relative efficiency of gas inflows from these two processes. We use two indicators of gas inflow: star formation rate (SFR) and gas phase metallicity, which are both measured relative to control samples. Whereas the metallicity of galaxy pairs is suppressed relative to its control sample of isolated galaxies, galaxies with bars are metal-rich for their stellar mass by 0.06 dex over all stellar masses. The SFRs of both the close galaxy pairs and the barred galaxies are enhanced by ~60%, but in the bars the enhancement is only seen at stellar masses M* >10^10 M_solar. Taking into account the relative frequency of bars and pairs, we estimate that at least three times more central star formation is triggered by bars than by interactions.