Cluster-Void Degeneracy Breaking: First Constraints and Future Prospects
Combining galaxy cluster and void abundances as cosmological probes helps break degeneracies between background evolution, growth of structure, and matter power-spectrum parameters. Complementarity in evolution, scale, density, degree of non-linearity provides multiple avenues for long constraining-power lever-arms. I demonstrate the first cosmological constraints derived from void abundance, which show that the joint existence of the largest known galaxy cluster and void is consistent with Planck and requires dark energy at >7 \sigma, independent of other dark-energy probes. I then discuss the power of combining galaxy cluster and void abundances as a means of constraining dark energy, modified gravity and neutrino properties with future large-scale surveys, in particular 4MOST, eRosita, Euclid and the Square Kilometer Array. One finds that the cluster-void combination has the potential to provide a competitive structure-only cosmological probe without the inclusion of e.g. cosmic microwave background data.
Based on ApjL 820(1), 7 (2016) , arXiv:1612.06595, Fundamental Physics with the SKA White Paper (in prep.), and other work in preparation.