http://arxiv.org/abs/2004.08406
We use self-similarity in N-body simulations of scale-free models to test for resolution dependence in the mass function and two-point correlation functions of dark matter halos. We use 1024$^3$ particle simulations performed with the ABACUS N-body code and define halos with two different algorithms, “friends of friends” (FOF) and ROCKSTAR. The FOF mass functions show a systematic deviation from self-similarity which is explained by a resolution dependence of the FOF mass assignment previously reported in the literature. Evidence for convergence is observed only starting from halos of several thousand particles, and mass functions are overestimated by as much as 20-25 percent for halos of 50 particles. The mass function of ROCKSTAR halos, on the other hand, shows good convergence from of order 50 to 100 particles per halo, with no detectable evidence at the one percent level of any systematic dependence for larger particle number. Tests show that the mass unbinding procedure in ROCKSTAR is the key factor in obtaining this much improved resolution. Applying the same analysis to the halo-halo two point correlation function, we find again strong evidence for convergence only for ROCKSTAR halos, at separations sufficiently large so that halos do not overlap. At these separations we can exclude dependence on resolution at the few percent level once halos have of order 50 to 100 particles. At smaller separations results are not converged even at significantly larger particle number, and bigger simulations would be required to establish the resolution required for convergence.
M. Leroy, L. Garrison, D. Eisenstein, et. al.
Tue, 21 Apr 20
15/90
Comments: 8 pages, 8 figures, submitted, comments welcome