Gravitational-wave Constraints on the Cosmic Opacity at z ∼ 5: Forecast from Space Gravitational-wave Antenna DECIGO

Abstract

Abstract Since gravitational waves (GWs) propagate freely through a perfect fluid, coalescing compact binary systems as standard sirens allow us to measure the luminosity distance directly and provide distance measurements unaffected by the cosmic opacity. DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a future Japanese space gravitational-wave antenna sensitive to frequency range between target frequencies of the Laser Interferometric Space Antenna and ground-based detectors. Combining the predicted future GW observations from DECIGO and three current popular astrophysical probes (H ii regions, SNe Ia Pantheon sample, quasar sample) in electromagnetic domains, one would be able to probe the opacity of the universe at different redshifts. In this paper, we show that the cosmic-opacity parameter can be constrained to a high precision (Δϵ ∼ 10−2) out to high redshifts (z ∼ 5). In order to reconstruct the evolution of cosmic opacity without assuming any particular functional form of it, the cosmic-opacity tests should be applied to individual redshift bins independently. Therefore, we also calculate the optical depth at individual redshifts and averaged τ(z) within redshift bins. Our findings indicate that, compared with the results obtained from the H ii galaxies and Pantheon SNe Ia, there is an improvement in precision when the quasar sample is considered. While nonzero optical depth is statistically significant only for redshift ranges 0 < z < 0.5, 1 < z < 2, and 2.5 < z < 3.5, such a tendency is different from that obtained in the framework of its parameterized form. Therefore, the importance of a cosmic-opacity test without a prescribed phenomenological function should be emphasized.