Other
Scientific paper
Nov 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........8s&link_type=abstract
Ph.D dissertation, 2005. Section 0190, Part 0606 118 pages; United States -- New Jersey: Rutgers The State University of New Je
Other
3
Spiral Galaxies, Warps
Scientific paper
This thesis presents two new studies of different aspects of disk galaxy dynamics using high-quality N -body simulations.
The first part of the thesis is a systematic study of the effects of central mass concentrations (CMCs) on bars. We find that bars are more robust than previously thought; the central mass has to be as large as several percent of the disk mass to completely destroy the bar on a short timescale. For a given mass, dense objects cause the greatest reduction in bar amplitude, while significantly more diffuse objects have a lesser effect. The bar is generally weakened by a CMC in two phases---the first phase of bar-weakening is due to the destruction by the CMC of lower-energy, bar-supporting orbits, while the second phase is a consequence of secular changes to the global potential which further diminish the number of bar-supporting orbits. We provide detailed phase-space and orbit analysis to support this suggestion. Our findings show that neither typical supermassive black holes in spirals nor typical central molecular gas concentrations should weaken the bar significantly within a Hubble time.
In the second part of the thesis, we study galactic warps formed through an idealized form of cosmic infall onto a disk galaxy. We find warps that closely resemble those observed and are in agreement with Briggs (1990)'s rules. The inner disk tilts remarkably rigidly, indicating strong cohesion due to self- gravity. The line of nodes of the warp inside R 26.5 ~ 4.5 R d is straight, while that beyond R 26.5 generally forms a loosely-wound, leading spiral in agreement with Briggs's rules. We focus on the mechanism of the warp and show that the leading spiral arises from the torques from the misaligned inner disk and its associated inner oblate halo. The warp is not strongly damped by the halo because the precession rate of the inner disk is slow and the inner halo generally remains aligned with the inner disk. Thus warps formed this way can persist for a few Gyrs, by which time another infall event can be expected.
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