How can gravitational-wave standard sirens and 21 cm intensity mapping jointly provide a precise late-universe cosmological probe?

Abstract

In the next decades, the gravitational-wave (GW) standard siren observations and the neutral hydrogen 21 cm intensity mapping (IM) surveys, as two promising non-optical cosmological probes, will play an important role in precisely measuring cosmological parameters. In this work, we make a forecast for cosmological parameter estimation with the synergy between the GW standard siren observations and the 21 cm IM surveys. We choose the Taiji observatory and the Einstein Telescope (ET) as the representatives of the GW detection projects and choose the Square Kilometre Array (SKA) phase I mid-frequency array as the representative of the 21 cm IM experiments. We find that the synergy of the GW standard siren observations and the 21 cm IM surveys could break the cosmological parameter degeneracies. The joint Taiji+ET+SKA data give σ(H0) = 0.23 km s −1 Mpc −1 in the ΛCDM model, σ(w) = 0.025 in the wCDM model, and σ(w0) = 0.057 and σ(wa) = 0.275 in the CPL model, which are better than the results of P lanck 2018 TT,TE,EE+lowE+lensing+SNe+BAO. In the ΛCDM model, the constraint accuracies of H0 and Ωm are less than or rather close to 1%, indicating that the magnificent prospects for non-optical precision cosmology are worth expecting.

Prospects for measuring dark energy with 21 cm intensity mapping experiments

“…In Ref. [82], Jin et al predicted that the synergy between the gravitational-wave standard siren observations based on Taiji + Cosmic Explorer and the 21 cm IM surveys based on SKA1 could achieve σ(w 0 ) = 0.077 and σ(w a ) = 0.30, which are 64% and 81% better than the results of Taiji + Cosmic Explorer. The above analysis shows that it is very beneficial to combine with 21 cm IM experiments for other observations in improving cosmological parameter estimation.…”

“…In recent years, most forecasts for cosmological parameter estimation with 21 cm IM experiments have assumed perfect foreground removal (e.g., Refs. [22,24,25,59,[82][83][84][85]), with exceptions (e.g., Refs. [23,36,86]).…”