Constraints on Non-Gaussianity from Sunyaev--Zeldovich Cluster Surveys

TL;DR

This paper forecasts how well Sunyaev-Zeldovich cluster surveys can constrain primordial non-Gaussianity, especially the nl parameter, using cluster counts and clustering, with a focus on scale-dependent halo bias.

Contribution

It provides a detailed Fisher matrix forecast for nl constraints from various SZ surveys, highlighting the importance of halo bias and survey coverage.

Findings

Planck cluster catalog constrains nl to 7 at 68% CL.

Halo bias provides stronger constraints than number counts.

Full-sky surveys are more effective for detecting non-Gaussianity.

Abstract

We perform a Fisher matrix analysis to forecast the capability of ongoing and future Sunyaev-Zeldovich cluster surveys in constraining the deviations from Gaussian distribution of primordial density perturbations. We use the constraining power of the cluster number counts and clustering properties to forecast limits on the $\fnl$ parameter. The primordial non-Gaussianity effects on the mass function and halo bias are considered. We adopt self-calibration for the mass-observable scaling relation, and evaluate constraints for the SPT, Planck, CCAT--like, SPTPol and ACTPol surveys. We show that the scale-dependence of halo bias induced by the local NG provides strong constraints on $\fnl$, while the results from number count are two orders of magnitude worse. When combining information from number counts and power spectrum, the \planck\ cluster catalog provides the tightest constraint with $\sigma_{\fnl}=7$ (68% C.L.) even for relatively conservative assumptions on the expected cluster yields and systematics. This value is a factor of 2 smaller than the $1\sigma$ error as measured by WMAP CMB measurements, and comparable to what expected from Planck. We find that the results are mildly sensitive to the mass threshold of the surveys, but strongly depend on the survey coverage: a full-sky survey like Planck is more favorable because it can probe longer wavelengths modes which are most sensitive to NG effects. In addition, the constraints are largely insensitive to priors on nuisance parameters as they are mainly driven by the power spectrum probe which has a mild dependence on the mass-observable relations.