Dependence of Halo Properties on Interaction History, Environment, and Cosmology

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Abstract
I present results from numerical N-body simulations regarding the effect of merging events on the angular momentum distribution of galactic halos, as well as a comparison of halo growth in Press-Schechter versus N-body methods. A total of six simulations are used, spanning three cosmologies: a standard flat Ω0 = 1 model, an open Ω0 = 0.3 model, and a "tilted" flat Ω0 = 1 model with spectral index n = 0.8. In each model, one run was conducted using a spatially uniform grid of particles and one using a refined grid in a large void. In all three models and all environments tested, the mean angular momentum of merger remnants (halo interaction products with mass ratios 3 : 1 or less) is greater than nonmerger remnants. Furthermore, the dispersion in the merger-remnant angular momentum distribution is smaller than the dispersion of the nonmerger distribution. The interpretation most consistent with the data is that the orbital angular momentum of the interactors is important in establishing the final angular momentum of the merger product. I give the angular momentum distribution, which describes the merger remnant population. I trace the most massive progenitor of L* galactic-mass halos (uniform grid) and 1011 M☉ halos (refined void) from z = 0 back to z = 5. Monte Carlo mass histories match simulations reasonably well for the latter sample. I find that for halos of mass 1012 M 1014 M☉, this method can underestimate the mass of progenitors by 20%, hence yielding improper formation redshifts of halos. With this caveat, however, the general shapes of halo mass histories and formation time distributions are preserved.

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