Multi-spectral Sirens: Gravitational-wave Cosmology with (Multi-) Sub-populations of Binary Black Holes

TL;DR

This paper introduces a novel multi-spectral siren method to measure the cosmic expansion rate using gravitational-wave data from subpopulations of binary black holes, demonstrating improved precision over traditional methods.

Contribution

The work proposes and validates a new approach to constrain the Hubble constant by leveraging subpopulations of GW events, enhancing measurement accuracy compared to existing spectral siren techniques.

Findings

Multi-spectral sirens provide about 19% tighter constraints on H_0 than traditional spectral sirens.

Application to GWTC-3 data yields H_0=73.3^{+29.9}_{-25.6} km/s/Mpc.

Including GW170817 improves H_0 measurement by approximately 23-26%.

Abstract

The cosmic expansion rate can be directly measured with gravitational-wave (GW) data of the compact binary mergers by jointly constraining the mass function of the population and the cosmological model via the so-called spectral sirens. Such a method relies on the features in the mass functions, which may originate from some individual subpopulations, and hence become blurred/indistinct due to the superposition of different subpopulations. In this work we propose a novel approach to constrain the cosmic expansion rate with subpopulations of GW events, named multi-spectral sirens. The advantage of the multi-spectral sirens compared to the traditional spectral sirens is demonstrated by the simulation with the mock data. The application of this approach to the GWTC-3 data yields $H_0=73.3^{+29.9}_{-25.6}~{\rm Mpc}^{-1}~{\rm km}~{\rm s}^{-1}$ (median and symmetric 68.3\% credible interval), which is about 19\% tighter than the result inferred with the traditional spectral sirens utilizing a PowerLaw+Peak mass function. The incorporation of the bright standard siren GW170817 with a uniform prior in [10,200] (log-uniform prior in [20,140]) ${\rm Mpc}^{-1}~{\rm km}~{\rm s}^{-1}$ gives $H_0=71.1^{+15.0}_{-7.5}~(70.3^{+12.9}_{-7.1})~{\rm Mpc}^{-1}~{\rm km}~{\rm s}^{-1}$ (68.3\% confidence level), corresponding to an improvement of $\sim26\%$ (23\%) with respect to the measurement from sole GW170817.