3 years ago

Probing Cosmology with Dark Matter Halo Sparsity Using X-ray Cluster Mass Measurements.

S. Ettori, Y. Rasera, S. Amodeo, M. Sereno, M.-A. Breton, D. Eckert, P.S. Corasaniti, V. Ghirardini

We present a new cosmological probe for galaxy clusters, the halo sparsity. This characterises halos in terms of the ratio of halo masses measured at two different radii and carries cosmological information encoded in the halo mass profile. Building upon the work of Balmes et al. (2014) we test the properties of the sparsity using halo catalogs from a numerical N-body simulation of ($2.6$ Gpc/h)$^3$ volume with $4096^3$ particles and show that the average sparsity value can be predicted from prior knowledge of the halo mass function. This provides a quantitative framework to infer cosmological parameter constraints using measurements of the sparsity of galaxy clusters. We show this point by performing a likelihood analysis of a synthetic sparsity dataset from which we recover the input fiducial cosmology. We evaluate the sparsity for a sample of X-ray clusters with hydrostatic mass estimates and derive constraints on the cosmic matter density $\Omega_m$ and the normalisation amplitude of density fluctuations at the $8$ Mpc h$^{-1}$ scale, $\sigma_8$. We find $\Omega_m=0.42\pm 0.17$ and $\sigma_8=0.80\pm 0.31$ at $1\sigma$. Future cluster surveys may provide opportunities for precise measurements of the sparsity. We forecast cosmological parameter errors for different sparsity observational scenarios and find that a sample of a few hundreds clusters with mass estimate errors at a few percent level can provide competitive cosmological parameter constraints complementary to those inferred from other cosmic probes.

Publisher URL: http://arxiv.org/abs/1711.00480

DOI: arXiv:1711.00480v1

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