BAR DISSOLUTION AND BULGE FORMATION - AN EXAMPLE OF SECULAR DYNAMICALEVOLUTION IN GALAXIES

We discuss secular changes in the stellar distribution in a barred dis k galaxy that may result from substantial inflows of gas. We present t wo- and three-dimensional N-body simulations of a disk galaxy in which we mimic the build up of gas at the center after a strong bar has for med. We show that the bar dissolves quickly and almost completely if t he core mass exceeds similar to 5% of the combined disk and bulge mass of the galaxy model we adopt. While this result agrees with our previ ous single-particle orbit calculations, the exact fraction for bar dis solution may well depend on the galaxy model adopted and requires furt her study. Bar formation and subsequent thickening and dissolution cre ates an additional bulgelike stellar component from the central part o f the disk. We build up the central concentration gradually, but the b ar dissolves abruptly once the sustaining orbits aligned with the bar become stochastic. We discuss the predictions of such a model, includi ng the point that barred Sc galaxies with sufficient central mass conc entrations should be building bulges now. We emphasize that bulges can originate from a number of different mechanisms and discuss current e vidence for bulge building and bar dissolution at both high and low re dshift. It is possible that bar formation, dissolution, and bulge buil ding may even be a recurrent process.