* Astronomy

Title: Galaxy Zoo: Bars in Disk Galaxies
Authors: Karen L. Masters (ICG, Portsmouth), Robert C. Nichol (ICG, Portsmouth), Ben Hoyle (ICG, Portsmouth/Barcelona), Chris Lintott (Oxford), Steven Bamford (Nottingham), Edward M. Edmondson (ICG, Portsmouth), Lucy Fortson (Adler Planetarium), William C. Keel (Alabama), Kevin Schawinski (Yale), Arfon Smith (Oxford), Daniel Thomas (ICG, Portsmouth)

We present first results from Galaxy Zoo 2, the second phase of the highly successful Galaxy Zoo project. 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 at higher redshift in the COSMOS survey, 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 classical bulges (which have a de Vaucouleurs profile) and pseudo-bulges (with exponential profiles) in disk galaxies.

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