Barred disks in dense environments

TL;DR

This study examines the properties and frequency of barred and unbarred disk galaxies in a dense cluster environment, revealing that bar presence correlates with galaxy luminosity and bulge prominence, with little variation across different cluster densities.

Contribution

It provides a detailed analysis of bar fractions in cluster disks using multiple selection methods, highlighting the importance of careful disk identification and the dependence of bars on galaxy properties.

Findings

Optical bar fraction is approximately 30% in the cluster.

Bar fraction increases in galaxies with no significant bulge.

No strong variation of bar fraction with local density within the cluster.

Abstract

We investigate the properties of bright (MV <= -18) barred and unbarred disks in the Abell 901/902 cluster system at z~0.165 with the STAGES HST ACS survey. To identify and characterize bars, we use ellipse-fitting. We use visual classification, a Sersic cut, and a color cut to select disk galaxies, and find that the latter two methods miss 31% and 51%, respectively of disk galaxies identified through visual classification. This underscores the importance of carefully selecting the disk sample in cluster environments. However, we find that the global optical bar fraction in the clusters is ~30% regardless of the method of disk selection. We study the relationship of the optical bar fraction to host galaxy properties, and find that the optical bar fraction depends strongly on the luminosity of the galaxy and whether it hosts a prominent bulge or is bulgeless. Within a given absolute magnitude bin, the optical bar fraction increases for galaxies with no significant bulge component. Within each morphological type bin, the optical bar fraction increases for brighter galaxies. We find no strong trend (variations larger than a factor of 1.3) for the optical bar fraction with local density within the cluster between the core and virial radius (R ~ 0.25 to 1.2 Mpc). We discuss the implications of our results for the evolution of bars and disks in dense environments.