5.5. Conclusion: Secular Evolution Processes in Barred Galaxies
I have reviewed recent progress toward an understanding of the many features seen in barred galaxies in terms of secular evolution processes driven by the bar. There are promising signs that even in complicated morphological descriptions such as (R)SB(rl)0 each symbol or feature has a well defined physical meaning. This is a first step toward a physical morphology of barred galaxies. The secular evolution processes identified to date are listed in Table 5. None of these processes is understood in detail. Furthermore, it is clear that such processes are concurrent and interdependent. For example, as long as a bar can grow by losing angular momentum to the disk, the signature of which is global spiral structure, it seems unlikely that it will evolve away by any interaction with the bulge. The study of secular evolution in barred galaxies is therefore a complicated problem which we have only begun to explore. However, the observations reviewed here support the idea that such evolution is taking place.
|Process||Raw Material||End Product|
|1. Heating by the bar||Disk stars||Exponential disk;|
|(Hohl 1971; Binney 1981a)||thicker disk|
|2. Evolution of bar to lens (?)||Bar stars||Lens|
|3. Dissipative rearranging of disk||Disk gas||Bulge and nucleus|
|material (see Roberts 1979a,b)||(4,5); inner ring;|
|4. Building up of the bulge with||Disk gas||Bulge|
|disk material (?)|
|5. Feeding the monster (?)||Disk gas||Nuclear activity|
|(Gunn 1977a; Simkin, Su and|
Stellar-dynamical studies of the bar itself are now making rapid progress. This is partly due to the fact that n-body modeling and absorption-line kinematic measurements are becoming reasonably routine. There are therefore good prospects for further progress, as observational and theoretical studies become detailed enough to stimulate and constrain each other.