The lure of sirens: joint distance and velocity measurements with third generation detectors

TL;DR

This paper explores how third-generation gravitational wave detectors can improve cosmological measurements by jointly analyzing distance and velocity data from binary neutron star mergers, enhancing constraints on key parameters.

Contribution

It introduces a comprehensive analysis framework for using standard sirens as both distance and density tracers, including new corrections and parameter considerations, for future cosmological studies.

Findings

Clustering analysis improves H0 constraints by 30%.

Density and velocity tracers significantly enhance spatial curvature measurements.

Projected precision of 0.1 km/s/Mpc for H0 with 5-year ET and Rubin data.

Abstract

The next generation of detectors will detect gravitational waves from binary neutron stars at cosmological distances, for which around a thousand electromagnetic follow-ups may be observed per year. So far, most work devoted to the expected cosmological impact of these standard sirens employed them only as distance indicators. Only recently their use as tracers of clustering, similar to what already proposed for supernovae, has been studied. Focusing on the expected specifications of the Einstein Telescope (ET), we forecast here the performance on cosmological parameters of future standard sirens as both distance and density indicators, with emphasis on the linear perturbation growth index and on spatial curvature. We improve upon previous studies in a number of ways: a more detailed analysis of available telescope time, the inclusion of more cosmological and nuisance parameters, the Alcock-Paczynski correction, the use of sirens also as both velocity and density tracers, and a more accurate estimation of the distance posterior. We find that the analysis of the clustering of sirens improves the constraints on $H_0$ by 30% and on $\Omega_{k0}$ by over an order of magnitude, with respect to their use merely as distance indicators. With 5 years of joint ET and Rubin Observatory follow-ups we could reach precision of 0.1 km/s/Mpc in $H_0$ and 0.02 in $\Omega_{k0}$ using only data in the range $0<z<0.5$. We also find that the use of sirens as tracers of density, and not only velocity, yields good improvements on the growth of structure constraints.