Galaxy Zoo: Bars in Disk Galaxies

TL;DR

This study analyzes the prevalence and characteristics of bars in disk galaxies using Galaxy Zoo 2 data, revealing correlations with galaxy color, luminosity, and bulge prominence, and discussing implications for galaxy evolution.

Contribution

First large-scale analysis of bar fractions in disk galaxies from Galaxy Zoo 2, linking bar presence to galaxy properties and evolution scenarios.

Findings

29.4% of disk galaxies have bars

Bar fraction increases with redder color and bulge prominence

Evidence of a color bimodality in disk galaxies

Abstract

We present first results from Galaxy Zoo 2, the second phase of the highly successful Galaxy Zoo project (www.galaxyzoo.org). Using a volume-limited sample of 13665 disk galaxies (0.01< z < 0.06 and M_r<-19.38), we study the fraction of galaxies with bars as a function of global galaxy properties like colour, luminosity and bulge prominence. Overall, 29.4+/-0.5% of galaxies in our sample have a bar, in excellent agreement with previous visually classified samples of galaxies (although this overall fraction is lower than measured by automated bar-finding methods). We see a clear increase in the bar fraction with redder (g-r) colours, decreased luminosity and in galaxies with more prominent bulges, to the extent that over half of the red, bulge-dominated, disk galaxies in our sample possess a bar. We see evidence for a colour bi-modality for our sample of disk galaxies, with a "red sequence" that is both bulge and bar-dominated, and a "blue cloud" which has little, or no, evidence for a (classical) bulge or bar. These results are consistent with similar trends for barred galaxies seen recently both locally and at higher redshift, and with early studies using the RC3. We discuss these results in the context of internal (secular) galaxy evolution scenarios and the possible links to the formation of bars and bulges in disk galaxies.