Bullet Clusters in the MareNostrum Universe

TL;DR

This paper uses large cosmological simulations to show that the observed dark matter-gas displacements in galaxy clusters, like the Bullet Cluster, are consistent with expectations in a Lambda CDM universe, and discusses future observational tests.

Contribution

It demonstrates that large displacements similar to the Bullet Cluster are expected in Lambda CDM simulations and explores their distribution across redshifts and cosmological parameters.

Findings

Displacements equal or larger than Bullet Cluster are expected in 1-2% of massive clusters.

Displacement distribution is similar across redshifts 0 to 0.5 when scaled appropriately.

Displacements are not highly sensitive to the normalization of the power spectrum.

Abstract

We estimate the expected distribution of displacements between the dark matter and gas cores in simulated clusters. We use the MareNostrum Universe, one of the largest non radiative, SPH Lambda CDM cosmological simulations. We find that projected 2-D displacements between dark matter and gas, equal or larger than the observed in the Bullet Cluster, are expected in 1% to 2% of the clusters with masses larger than 10^{14} Msun. The 2-D displacement distribution is roughly the same between redshifts 0<z<0.5 when multiplied by a factor of (1+z)^{-1/2}. We conclude that the separations between dark matter and gas as observed in the bullet cluster can be easily found in a Lambda CDM universe. Furthermore we find that the displacement distribution is not very sensitive to the normalization of the power spectrum. Upcoming surveys could extend the measurements of these displacements between dark matter and gas into large samples of hundreds of clusters, providing a potential test for Lambda CDM.