Tobias Géron

How does a bar affect its host? We investigate the effect of strong and weak bars in star forming galaxies in the context of galaxy quenching and galaxy evolution. The strong and weak bars in this study were identified using Galaxy Zoo DECaLS (GZD), the newest version of Galaxy Zoo, which uses imaging from the DECaLS survey. Our sample was also cross-matched against ALFALFA for gas mass measurements. In the end, we have a volume-limited sample (0.01 z 0.05, Mr −18.96) of 2,071 galaxies with reliable volunteer classifications.

We find a weak bar fraction of 28.3% and a strong bar fraction of 14.9%, resulting in a total barred fraction of 43.2%, consistent with the literature. Interestingly, we observed that the strong bar fraction is typically higher in quiescent galaxies than in star forming galaxies, whereas the weak bar fraction is similar in both groups. Additionally, we found that star forming galaxies with strong bars have higher fibre SFRs, lower gas masses and shorter depletion timescales, compared to unbarred star forming galaxies. The increase of SFR in the fibre is in agreement with previous theories stating that bars funnel gas to the centre, where it is used for star formation. This was not found for star forming galaxies with a weak bar. This shows that strong bars facilitate the quenching process and suggests that bar morphology plays an important role in the evolution of a galaxy.

Finally, we have also found that the differences between strong and weak bars that we observed, disappear when we control for bar length. We conclude that strong and weak bars are not fundamentally different phenomena, but instead we propose that there is a continuum of bar types, which varies from `weakest' to `strongest'.