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

TL;DR

This paper investigates how combining photometric galaxy surveys with 21cm intensity mapping can improve constraints on primordial non-Gaussianity, using multi-tracer analysis and Fisher forecasts to assess the impact of survey parameters.

Contribution

It extends previous work by combining photometric galaxy surveys with 21cm intensity mapping, including single-dish and interferometric modes, to enhance constraints on local-type non-Gaussianity.

Findings

Multi-tracer approach improves $f_{NL}$ constraints by up to 23%.

Interferometric 21cm surveys outperform single-dish modes in constraining $f_{NL}$.

Redshift range and sky area significantly affect the $f_{NL}$ constraints.

Abstract

The fluctuations produced during cosmic inflation may exhibit non-Gaussian characteristics that are imprinted in the large-scale structure of the Universe. This non-Gaussian imprint is an ultra-large scale signal that can be detected using the power spectrum. We focus on the local-type non-Gaussianity $f_{\rm{NL}}$ and employ a multi-tracer analysis that combines different probes in order to mitigate cosmic variance and maximize the non-Gaussian signal. In our previous paper, we showed that combining spectroscopic galaxy surveys with 21cm intensity mapping surveys in interferometer mode could lead to a $\sim 20-30\%$ improvement in the precision on this non-Gaussian signal. Here we combine the same 21 cm experiments, including also single-dish surveys, with photometric galaxy surveys. The 21 cm single-dish surveys are based on MeerKAT and SKAO and the interferometric surveys are alike to HIRAX and PUMA. We implement foreground-avoidance filters and utilize models for the 21 cm thermal noise associated with single-dish and interferometer modes. The photometric galaxy surveys are similar to the DES and LSST. Our multi-tracer Fisher forecasts show a better precision for the combination of the photometric galaxy surveys and 21 cm interferometric surveys than with the 21 cm single-dish surveys -leading to at most an improvement of $23\%$ in the former case and $16\%$ in the latter case. Furthermore, we examine the impact of varying the foreground filter parameter, redshift range and sky area on the derived constraint. We find that the $f_{\rm{NL}}$ constraint is highly sensitive to both the redshift range and sky area. The foreground filter parameter shows negligible effect.