Constraining primordial non-Gaussianity via a multitracer technique with surveys by Euclid and Square Kilometre Array

TL;DR

This paper forecasts how future galaxy surveys by Euclid and SKA, combined with multitracer techniques, can significantly improve constraints on primordial non-Gaussianity parameter $f_{NL}$, reaching uncertainties below 1.

Contribution

It derives a general covariance matrix expression for multitracer power spectra and demonstrates how survey combination enhances constraints on $f_{NL}$.

Findings

Constraints on $f_{NL}$ can be below 1 with a single survey.

Combining Euclid and SKA phase 1 yields $\sigma(f_{NL})=0.61$.

Combining Euclid and SKA phase 2 yields $\sigma(f_{NL})=0.50$.

Abstract

We forecast future constraints on local-type primordial non-Gaussianity parameter $f_{\rm NL}$ with a photometric galaxy survey by Euclid, a continuum galaxy survey by Square Kilometre Array (SKA), and their combination. We derive a general expression for the covariance matrix of the power spectrum estimates of multiple tracers to show how the so-called multitracer technique improves constraints on $f_{\rm NL}$. In particular we clarify the role of the overlap fraction of multiple tracers and the division method of the tracers. Our Fisher matrix analysis indicates that stringent constraints of $\sigma (f_{\rm NL})\lesssim 1$ can be obtained even with a single survey, assuming five mass bins. When Euclid and SKA phase 1 (2) are combined, constraints on $f_{\rm NL}$ are improved to $\sigma (f_{\rm NL})= 0.61~(0.50)$.