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

Abstract

I present results from numerical N-body simulations regarding the e †ect 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 Ñat model, an open model, and a "" tilted ÏÏ Ñat model with spectral) 0 \ 1) 0 \ 0.3) 0 \ 1 index n \ 0.8. In each model, one run was conducted using a spatially uniform grid of particles and one using a reÐned 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 Ðnal 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 galactic-mass halos (uniform L * grid) and 1011 halos (reÐned void) from z \ 0 back to z \ 5. Monte Carlo mass histories match M _ simulations reasonably well for the latter sample. I Ðnd that for halos of mass this 1012 [ M [ 1014 M _ , 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.