|Annu. Rev. Astron. Astrophys. 2004. 42:
Copyright © 2004 by Annual Reviews. All rights reserved
7.3. Demise of Bars. II. Is Pseudobulge Formation Self-Limiting?
If building a central mass concentration of 5 % - 10 % of the disk mass destroys the bar, does secular evolution then stop? Do we already know the maximum bulge-to-disk ratio B / D that secular evolution can produce?
The answer is probably "no". (1) Many SB0 and SBa galaxies have bulge-to-disk ratios of ~ 1. So bars can coexist with surprisingly large central mass concentrations. (2) Once bars grow non-linear, simple heuristic arguments about how to make a successful bar lose force. In particular, it may no longer be necessary that the radius of ILR be small. (3) The simulations that demonstrate bar suicide do not take into account enough physics. Many do not include gas. Almost none allow the bar to interact with all of the components that we see in galaxies. The competition between angular momentum sinks that help to strengthen bars and the damaging effects of pseudobulge building may be weighted more in favor of the angular momentum sinks than current simulations suggest. (4) Gravitational tickling of an unbarred galaxy with an encounter (but not a merger) may re-excite a bar (Noguchi 1988; Gerin, Combes, & Athanassoula 1990; Barnes & Hernquist 1991).
Pseudobulge building may be self-limiting, but it does not necessarily stop at the small bulge-to-disk ratios quoted above.