The signature of dark energy perturbations in galaxy cluster surveys

TL;DR

This paper investigates how dark energy fluctuations influence galaxy cluster counts and demonstrates that current and future surveys can detect or constrain these perturbations, providing insights into dark energy's nature.

Contribution

It introduces a generalized spherical collapse model and Fisher matrix analysis to assess dark energy perturbations' effects on galaxy cluster surveys.

Findings

Dark energy fluctuations can significantly affect cluster counts.

Current instruments like the South Pole Telescope can detect these effects.

Future surveys will better distinguish dark energy models based on perturbations.

Abstract

All models of dynamical dark energy possess fluctuations, which affect the number of galaxy clusters in the Universe. We have studied the impact of dark energy clustering on the number of clusters using a generalization of the spherical collapse model and the Press-Schechter formalism. Our statistical analysis is performed in a 7-parameter space using the Fisher matrix method, for several hypothetical Sunyaev-Zel'dovich and weak lensing (shear maps) surveys. In some scenarios, the impact of these fluctuations is large enough that their effect could already be detected by existing instruments such as the South Pole Telescope, when its data is combined with WMAP and SDSS. Future observations could go much further and probe the nature of dark energy by distinguishing between different models on the basis of their perturbations, not only their expansion histories.