Coma Cluster Treasury Survey

Project Overview - Objective 5

Disks, Bulges and Bars in the Cluster Environment

The high density in the Coma cluster core makes it an ideal place to investigate the morphology-density relation, which is such that elliptical galaxies are more common than spiral galaxies in dense environments. We know that average bulge-to-disk flux ratios and neutral hydrogen gas (HI) depletion increases with galaxy density in the Coma cluster. Using ground-based imaging, a recent analysis concluded that disks in the Coma core are roughly 1/3rd smaller than in the field for a given bulge size. The HST data will allow us to dramatically improve the quantitative basis for these statements, as bulge/disk decomposition in the presence of nuclear components depends critically on spatial resolution. The radial dependence within the Coma cluster of bulge and disk morphologies will constrain the roles of mergers and of disk truncation processes.

It is widely recognized that stellar bars redistribute the angular momentum of baryons and dark matter in disk galaxies, driving their dynamical and secular evolution. From a theoretical standpoint, we expect bars to occur in dynamically cold, gas-rich disks either spontaneously or under the influence of a satellite companion or a minor merger. In cluster environments, high speed impulsive encounters (minor mergers and harassment) and ram-pressure stripping exert competing influences on the formation and destruction of bars. We intend to identify unobscured primary and nuclear bars that can be as small as a few 100 parsecs, and detect nuclear features induced by bars, such as resonance starburst rings, compact disks, and disky pseudo-bulges. The properties (size, strengths, ellipticities) of bars will be characterized using rigorous quantitative criteria which have been previously applied to several thousand galaxies at z ~ 0.2-1 from the GEMS survey, demonstrating that optically visible bars are abundant out to z ~ 1. We will directly compare the derived optical bar properties in the Coma galaxies to matched control samples of galaxies in SDSS and GEMS.

While observations in the rest-frame I-band (F814W filter) may miss some highly obscured morphological features, a comparison of the optical properties across field and cluster environments will set important constraints on how environment influences their formation and evolution.