Dependence of Halo Properties on Interaction History, Environment and Cosmology

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 vs. N-body methods. A total of six simulations are used spanning 3 cosmologies: a standard flat Omega_0=1 model, an open Omega_0=0.3 model and a "tilted" flat Omega_0=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 non-merger remnants. Furthermore, the dispersion in the merger-remnant angular momentum distribution is smaller than the dispersion of the non-merger 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 10^{11} solar mass halos (refined void) from redshift 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 10^{12} to 10^{14} solar masses, 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.