Galaxy Zoo: Stronger bars facilitate quenching in star forming galaxies

TL;DR

This study uses Galaxy Zoo DECaLS data to analyze how strong and weak bars in disk galaxies influence star formation and quenching, revealing that strong bars are associated with quenching processes in star-forming galaxies.

Contribution

The paper provides a detailed comparison of strong and weak bars in galaxies, showing that bar strength correlates with quenching indicators and proposing a continuum model of bar types.

Findings

Strong bars are more common in quiescent galaxies.

Strong bars facilitate star formation quenching by reducing gas and increasing depletion.

Differences between strong and weak bars diminish when controlling for bar length.

Abstract

We have used Galaxy Zoo DECaLS (GZD) to study strong and weak bars in disk galaxies. Out of the 314,000 galaxies in GZD, we created a volume-limited sample (0.01 < z < 0.05, Mr < -18.96) which contains 1,867 galaxies with reliable volunteer bar classifications in the ALFALFA footprint. In keeping with previous Galaxy Zoo surveys (such as GZ2), the morphological classifications from GZD agree well with previous morphological surveys. GZD considers galaxies to either have a strong bar (15.5%), a weak bar (28.1%) or no bar (56.4%), based on volunteer classifications on images obtained from the DECaLS survey. This places GZD in a unique position to assess differences between strong and weak bars. We find that the strong bar fraction is typically higher in quiescent galaxies than in star forming galaxies, while the weak bar fraction is similar. Moreover, we have found that strong bars facilitate the quenching process in star forming galaxies, finding higher fibre SFRs, lower gas masses and shorter depletion timescales in these galaxies compared to unbarred galaxies. However, we also found that any differences between strong and weak bars disappear when controlling for bar length. Based on this, we conclude that weak and strong bars are not fundamentally different phenomena. Instead, we propose that there is a continuum of bar types, which varies from 'weakest' to 'strongest'.