Mathematics
Scientific paper
Jan 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.........1j&link_type=abstract
PhD Thesis, Combined Faculties for the Natural Sciences and for Mathematics of the University of Heidelberg, Germany. II + 82 pp
Mathematics
Galaxies, N-Body Simulations, Dark Matter, Galactic Halos, Stellar Dynamics
Scientific paper
We examine in this work two different formation mechanisms of galaxies in N-body simulations. Under the assumption that particles in a spherical dark matter halo move on circular orbits we can predict the amount of contraction of the dark matter halo during the slow formation of the disk with an adiabatic approximation. We find in N-body simulations that the adiabatic approximation is valid for all realistic mass ratios between dark matter halos and disk galaxies and that deviations from circular orbits cannot play a decisive role. In the second part we focus on the formation of ellipticals through mergers of disk galaxies. We classify the complex orbital structure in a sample of 150 collisions. The classification is correlated with shape parameters of an elliptical galaxy, such as its triaxiality or the ratios of its principal axes. We are deriving a global occupation probability for self-consistent triaxial galaxies which are in agreement with theoretical expectations. Furthermore we find that the isophotal structure of the merger remnants cannot be explained by one orbit class alone, but by a superposition of classes. The dichotomy of observed isophotal shape in boxy and disky elliptical galaxies, cannot be completely explained by the dominance of box-like, respectivley disk-like orbits in those galaxies. Current simulations cannot reproduce observed correlation between the h3 parameter and the mean velocity. We identify a central box orbit component as the reason for this discrepancy, which are overproduced in dissipationless simulations. The z-tube component follows the correlation very well. It follows also the observed correlation between the h3 parameter and v/σ0. We conclude that only one dynamical component is necessary to explain the observed correlations, which looks like a puffy disk with high velocity dispersion.
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