Computer Science
Scientific paper
Aug 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt.........2z&link_type=abstract
Thesis (PhD). THE JOHNS HOPKINS UNIVERSITY, Source DAI-B 62/02, p. 900, Aug 2001, 146 pages.
Computer Science
1
Scientific paper
The effects of viscosity and clumpiness are investigated in the context of the formation and the dynamical evolution of galaxies by analytical models and numerical simulations. The major motivation of this investigation is to study how these two factors can alter the angular momentum behavior of the galaxies formed in the bottom-up formation scenario as indicated by the hierarchical CDM cosmology. We analytically modify the standard disk formation model to incorporate the effect of viscous evolution. We derive generic analytic solutions for the disk-halo system after adiabatic compression of the dark halo, with free choice of the input virialized dark halo density profile and of the specific angular momentum distribution. We derive limits on the final density profile of the halo in the central regions due to the condensation of gas. The viscous evolution can redistribute angular momentum distribution by driving material inwards to form a proto- bulge which can be formed by the bar instability in the proto-disk, and by spreading gas to large radius to form pure exponential stellar disk if the viscous evolution timescale and star formation timescale are similar. The `disk-halo' conspiracy is found to be formed better by the disk-halo interaction during the viscous evolution of disk. We investigate the relationship between the assumed initial conditions, such as halo `formation', or assembly, redshift zf, spin parameter λ, baryonic fraction F, and final disk properties such as global star formation timescale, gas fraction, and bulge-to-disk ratio. We find that the present properties of disks, such as the scale length, are compatible with a higher initial formation redshift if the re-distribution by viscous evolution is included than if it is ignored. The numerical simulations confirm many results derived in the analytical model. Further it is found that pure viscous evolution can be unstable. Possibly feedback from star formation is required to maintain a stable viscous evolution. The evolution of clumpy structure embedded in non- dissipative dark halos is studied through N-body simulations of isolated systems. We determine by both analytic calculations and direct analysis of the N-body simulations the relative importance of various dynamical processes acting on the clumps. (Abstract shortened by UMI.)
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