Constraining primordial non-Gaussianity by combining next-generation galaxy and 21 cm intensity mapping surveys

TL;DR

This paper demonstrates that combining galaxy and 21 cm intensity mapping surveys with a multi-tracer approach can significantly improve constraints on primordial non-Gaussianity, achieving precision comparable to the CMB.

Contribution

It introduces a multi-tracer method combining optical galaxy and 21 cm surveys to better constrain primordial non-Gaussianity, accounting for systematic foreground effects.

Findings

Multi-tracer approach reduces cosmic variance in non-Gaussianity measurements.

Forecasted precision on $f_{NL}$ is around 4 with systematic considerations.

Combination of surveys can match CMB constraints on primordial non-Gaussianity.

Abstract

Surveys of the matter distribution contain `fossil' information on possible non-Gaussianity that is generated in the primordial Universe. This primordial signal survives only on the largest scales where cosmic variance is strongest. By combining different surveys in a multi-tracer approach, we can suppress the cosmic variance and significantly improve the precision on the level of primordial non-Gaussianity. We consider a combination of an optical galaxy survey, like the recently initiated DESI survey, together with a new and very different type of survey, a 21 cm intensity mapping survey, like the upcoming SKAO survey. A Fisher forecast of the precision on the local primordial non-Gaussianity parameter $f_{\mathrm{NL}}$, shows that this multi-tracer combination, together with non-overlap single-tracer information, can deliver precision comparable to that from the CMB. Taking account of the largest systematic, i.e. foreground contamination in intensity mapping, we find that $\sigma(f_{\mathrm{NL}}) \sim 4$.