The Formation and Evolution of Bars, and Its Impact on Galaxy Dynamics

Abstract

Observations of galaxies show that in the nearby universe we see that approximately 2/3 of the disk galaxies are barred ones (Eskridge et al., 2000). The formation and evolution scenarios of bars are mainly studied with N-body simulations. In an isolated disk galaxy which is rotationally supported, the disk tends to form a bar as it has globally unstable modes (Kalnajs, 1972). It has been suggested that a massive halo surrounding the disk can stabilize it against bar type instabilities (Ostriker & Peebles, 1973) by increasing the random motion of the stars. There are several other studies which claims that central mass concentration may not allow bars to form. It is also known that as disks become bar unstable, it transport the angular momentum from the inner disk to outer disk as well as to the surrounding dark matter halo. In this thesis we have studied bar formation and evolution using N-body simulations. We have focused on the effect of bulge mass and concentration on bar formation and evolution, and derived a new bar formation criterion. We also tested the criterion with observations collected from literature. We then investigated the effect of bulge mass on bar pattern speed since observations do not give a clear idea of the nature and origin of slow and fast of bars in galaxies. Bars also a potential candidate for changing the dark matter profile in the central regions of galaxies as they transports angular momentum from disk to the dark halo. We have also studied this effect using N-body simulations.