LiteBIRD Science Goals and Forecasts. Mapping the Hot Gas in the Universe

TL;DR

This paper evaluates LiteBIRD's ability to map the hot gas in the universe via the thermal SZ effect, demonstrating improved sensitivity and foreground mitigation when combined with Planck data, leading to tighter cosmological constraints.

Contribution

It introduces a tailored component-separation pipeline combining LiteBIRD and Planck data to produce an all-sky thermal SZ map with enhanced sensitivity and foreground removal.

Findings

LiteBIRD enables full-sky thermal SZ mapping with reduced foreground contamination.

Combining LiteBIRD with Planck improves the precision of cosmological parameters by 15%.

Effective mitigation of LiteBIRD's 1/f noise below the SZ signal across all multipoles.

Abstract

We assess the capabilities of the LiteBIRD mission to map the hot gas distribution in the Universe through the thermal Sunyaev-Zeldovich (SZ) effect. Our analysis relies on comprehensive simulations incorporating various sources of Galactic and extragalactic foreground emission, while accounting for specific instrumental characteristics of LiteBIRD, such as detector sensitivities, frequency-dependent beam convolution, inhomogeneous sky scanning, and $1/f$ noise. We implement a tailored component-separation pipeline to map the thermal SZ Compton $y$-parameter over 98% of the sky. Despite lower angular resolution for galaxy cluster science, LiteBIRD provides full-sky coverage and, compared to the Planck satellite, enhanced sensitivity, as well as more frequency bands to enable the construction of an all-sky $y$-map, with reduced foreground contamination at large and intermediate angular scales. By combining LiteBIRD and Planck channels in the component-separation pipeline, we obtain an optimal $y$-map that leverages the advantages of both experiments, with the higher angular resolution of the Planck channels enabling the recovery of compact clusters beyond the LiteBIRD beam limitations, and the numerous sensitive LiteBIRD channels further mitigating foregrounds. The added value of LiteBIRD is highlighted through the examination of maps, power spectra, and one-point statistics of the various sky components. After component separation, the $1/f$ noise from LiteBIRD is effectively mitigated below the thermal SZ signal at all multipoles. Cosmological constraints on $S_8=\sigma_8\left(\Omega_{\rm m}/0.3\right)^{0.5}$ obtained from the LiteBIRD-Planck combined $y$-map power spectrum exhibits a 15% reduction in uncertainty compared to constraints from Planck alone. This improvement can be attributed to the increased portion of uncontaminated sky available in the LiteBIRD-Planck combined $y$-map.