Arc statistics with realistic cluster potentials. IV. Clusters in different cosmologies

TL;DR

This study uses simulations to compare how different cosmological models affect galaxy clusters' ability to produce large gravitational arcs, finding that OCDM best matches observed arc abundance.

Contribution

It provides a comparative analysis of arc formation in various cosmologies using realistic cluster potentials and simulations.

Findings

OCDM model best reproduces observed arc abundance.

LambdaCDM underpredicts arc formation by about two orders of magnitude.

Differences are due to cluster formation epochs and lensing non-linearity.

Abstract

We use numerical simulations of galaxy clusters in different cosmologies to study their ability to form large arcs. The cosmological models are: Standard CDM (SCDM; Omega_0=1, Omega_Lambda=0); tauCDM with reduced small-scale power (parameters as SCDM, but with a smaller shape parameter of the power spectrum); open CDM (OCDM; Omega_0=0.3, Omega_Lambda=0); and spatially flat, low-density CDM (LambdaCDM; Omega_0=0.3, Omega_Lambda=0.7). All models are normalised to the local number density of rich clusters. Simulating gravitational lensing by these clusters, we compute optical depths for the formation of large arcs. For large arcs with length-to-width ratio >= 10, the optical depth is largest for OCDM. Relative to OCDM, the optical depth is lower by about an order of magnitude for LambdaCDM, and by about two orders of magnitude for S/tauCDM. These differences originate from the different epochs of cluster formation across the cosmological models, and from the non-linearity of the strong lensing effect. We conclude that only the OCDM model can reproduce the observed arc abundance well, while the other models fail to do so by orders of magnitude.