Secondary-Mass Features improve Spectral-Siren $H_0$ Constraints

TL;DR

This study introduces a new model for secondary masses in gravitational-wave sources, improving H_0 measurements from spectral sirens and highlighting the importance of secondary mass features for cosmology.

Contribution

It presents a flexible parametric model for secondary mass distribution, enhancing H_0 constraints from GW data and emphasizing the role of secondary masses in cosmological inference.

Findings

H_0 = 71.4^{+13.8}_{-13.4} km/s/Mpc from spectral sirens alone

H_0 = 73.5^{+9.2}_{-7.2} km/s/Mpc when combined with GW170817

Features like peaks near 18 M_sun and 65 M_sun improve H_0 precision

Abstract

Gravitational-wave (GW) signals from compact binary coalescences (CBCs) enable independent measurements of the Hubble constant \(H_0\) via the spectral siren method, which critically depends on an accurate model of the source-frame mass distribution. While the primary mass function has been extensively studied, the impact of the secondary mass distribution on cosmological inference has been largely overlooked. Here, we perform a joint inference of population and cosmological parameters using 142 confident CBC detections from GWTC-4.0, adopting a new parametric model that flexibly describes features in both the component-mass spectrum and the pairing function, with particular emphasis on the secondary masses. We find \(H_0 = 71.4^{+13.8}_{-13.4} \;\mathrm{km\,s^{-1}\,Mpc^{-1}}\) (68\% CL) from spectral sirens alone, and \(H_0 = 73.5^{+9.2}_{-7.2} \;\mathrm{km\,s^{-1}\,Mpc^{-1}}\) when combined with the bright siren GW170817. Compared to the standard LVK Fullpop-4.0 analysis, these constraints represent improvements of \(\sim29.8\%\) and \(\sim22.2\%\) in \(H_0\) uncertainty, respectively. The enhanced precision is driven by previously unmodeled features, including peaks near \(18\,M_\odot\) and \(65\,M_\odot\) as well as mass-dependent pairing transitions at \(28\,M_\odot\) and \(52\,M_\odot\). Our results demonstrate that the secondary mass function is also a key ingredient for precision standard siren cosmology.