X-ray Cluster Constraints on Non-Gaussianity

TL;DR

This paper derives constraints on primordial non-Gaussianity using X-ray cluster data, incorporating higher moments beyond skewness, and demonstrates the potential of cluster counts to differentiate inflation models.

Contribution

It introduces an analytic method to include higher cumulants in the cluster mass function and provides the first large-scale structure constraints on non-Gaussianity applicable to inflation models.

Findings

Current data constrains non-Gaussianity parameters at a useful level.

Cluster counts can distinguish models with identical bispectra.

Constraints on fNL are comparable to other large-scale structure probes.

Abstract

We report constraints on primordial non-Gaussianity from the abundance of X-ray detected clusters. Our analytic prescription for adding non-Gaussianity to the cluster mass function takes into account moments beyond the skewness, and we demonstrate that those moments should not be ignored in most analyses of cluster data. We constrain the amplitude of the skewness for two scenarios that have different overall levels of non-Gaussianity, characterized by how amplitudes of higher cumulants scale with the skewness. We find that current data can constrain these one-parameter non-Gaussian models at a useful level, but are not sensitive to adding further details of the corresponding inflation scenarios. Combining cluster data with Cosmic Microwave Background constraints on the cosmology and power spectrum amplitude, we find the dimensionless skewness to be 1000*M3=-1+24-28 for one of our scaling scenarios, and 1000*M3=-4+/-7 for the other. These are the first constraints on non-Gaussianity from Large Scale Structure that can be usefully applied to any model of primordial non-Gaussianity. When applied to the standard local ansatz, the constraint corresponds to fNL=-3+78-91. When applied to a model with a local-shape bispectrum but higher cumulants that are relatively more important, the amplitude of the local-shape bispectrum is constrained to be fNL=-14+22-21. This sensitivity implies that cluster counts could be used to distinguish qualitatively different models for the primordial fluctuations that have identical bispectra. (Abstract Abridged.)