Abstract
We study the abundance of clusters in the LasDamas suite of cosmological N-body simulations. These simulations contain an unprecedented volume (750 Gpc3/h3) and are seeded with initial conditions using second order lagrangian perturbation theory (2LPT) instead of the standard Zel'Dovich approximation (ZA). Recent results show that ZA leads to unphysical transients that predominantly inhibit the collapse of the earliest forming density peaks such as massive halos of galaxy clusters. We compare our results to simulations seeded with ZA, but using the same starting redshift, cosmology, simulation parameters, and phases. We find a significant systematic bias in the number density of clusters that grows with both halo mass and redshift. For masses greater than 2e14 Msun/h, we find that ZA underpredicts the abundance of halos by 3% at z=0 and 15% at z=1. For masses greater than 5e14 Msun/h, these rise to 5% and 20%, respectively. We show that this bias is only partially mitigated by using ZA with a higher starting redshift. We demonstrate the effect on cluster abundance persists regardless of halo defintion, quantifying the effect for both spherical overdensity and friends-of-friends halos. If unaccounted for, this bias can lead to inaccurate cosmological constraints on dark energy, or be misinterpreted as primordial non-Gaussianity.
McBride, C