First cosmological constraints combining Planck with the recent gravitational-wave standard siren measurement of the Hubble constant

TL;DR

This paper combines gravitational-wave standard siren measurements with Planck CMB data to improve constraints on the Hubble constant and other cosmological parameters within an extended ΛCDM model.

Contribution

First integration of GW170817 standard siren data with Planck observations in a 12-parameter cosmological model, refining bounds on H_0 and related parameters.

Findings

GW170817 measurement reduces the allowed parameter space.

Including GW data improves bounds on neutrino mass, curvature, and dark energy.

H_0 constrained to 55^{+7}_{-20} km/s/Mpc at 68% CL when combined.

Abstract

The recent observations of gravitational-wave and electromagnetic emission produced by the merger of the binary neutron-star system GW170817 have opened the possibility of using standard sirens to constrain the value of the Hubble constant. While the reported bound of $H_0=70_{-8}^{+12}$ at $68 \%$ C.L. is significantly weaker than those recently derived by observations of Cepheid variables, it does not require any form of cosmic distance ladder and can be considered as complementary and, in principle, more conservative. Here we combine, for the first time, the new measurement with the Planck Cosmic Microwave Background observations in a $12$ parameters extended $\Lambda$CDM scenario, where the Hubble constant is weakly constrained from CMB data alone and bound to a low value $H_0=55^{+7}_{-20}$ km/s/Mpc at $68 \%$ C.L. We point out that the non-Gaussian shape of the GW170817 bound makes lower values of the Hubble constant in worst agreement with observations than what expected from a Gaussian form. The inclusion of the new GW170817 Hubble constant measurement therefore significantly reduces the allowed parameter space, improving the cosmological bounds on several parameters as the neutrino mass, curvature and the dark energy equation of state.