Galaxies are self-gravitating structures composed of stars, gas and dark matter, and are the basic building blocks of structure in the universe. They are home to virtually all of the known astronomical objects, whose history is coupled to that of the host. Galactic evolution is highly non-linear, being driven by processes which redistribute mass on both dynamical and cosmological timescales. Developing a comprehensive understanding of their formation and evolution is one of the most important and fundamental problems in astronomy.

 

It has become evident with the availability of near-infrared imaging that a bar or oval distortion is a common feature of disk galaxies. The presence of such non-axisymmetries, whether triggered by an external interaction or formed through an internal global instability, will have significant evolutionary implications for a host galaxy. The torque produced by such features is an efficient mechanism to bring large quantities of disk gas into the inner regions, providing the required fuel for an Active Galactic Nucleus (AGN). On the other hand, bars create resonances which retard the inward flow of gas and promote vigorous star formation which may consume a large fraction of the gas. Bars may as well play a role in bulge building through the creation of vertical resonances. However, the build up of mass at the center weakens and will eventually destroy the bar. Though the interplay between these processes is still poorly understood, the overall effect is likely to be a bar driven morphological change from late to early disk type. It is just such observed changes which are at the center of the current debate on the evolution of galaxies over cosmological timescales.

 

Also, issues related to the dark matter (DM) halo formation and evolution have wide implications for kinematics and dynamics of galactic disks that grow in their midst. As baryonic matter accumulates to form the disk its orbits are shaped by the gravitational potential of the halo. However, the mass distribution of early halos is likely to be triaxial. This triaxiality will produce a torque on the forming disk, causing shocks to form and the highly dissipative gas to flow inward. The gravity of the accumulating gas will reduce the triaxiality of the potential at the center of galaxy and over time modify the mass distribution of the inner halo.

 

Star formation and its associated feedback of energy through young stellar winds and supernovae also plays an important role in the evolution of galaxies. The spatial distribution and rate of star formation is greatly influenced by the local and global dynamics of the system, while the dynamics are continually modified by the star formation through the deposition of stellar mass and the flow of gas. This complicated coupling is poorly understood, yet is the key to future progress in understanding galaxy formation and evolution. The introduction of these fundamental processes into numerical simulations is in its infancy and represents the next major advancement in this field.