Unbiased Hubble constant estimation from binary neutron star mergers

Abstract

Gravitational wave (GW) observations of binary neutron star (BNS) mergers can be used to measure luminosity distances and hence, when coupled with estimates for the mergers' host redshifts, infer the Hubble constant, H0. These observations are, however, affected by GW measurement noise, uncertainties in host redshifts and peculiar velocities, and are potentially biased by selection effects and the mis-specification of the cosmological model or the BNS population. The estimation of H0 from samples of BNS mergers with optical counterparts is tested here by using a phenomenological model for the GW strains that captures both the data-driven event selection and the distanceinclination degeneracy, while being simple enough to facilitate large numbers of simulations. A rigorous Bayesian approach to analyzing the data from such simulated BNS merger samples is shown to yield results that are unbiased, have the appropriate uncertainties, and are robust to model misspecification. Applying such methods to a sample of N 50 BNS merger events, as LIGO+Virgo could produce in the next ∼ 5 years, should yield robust and accurate Hubble constant estimates that are precise to a level of < ∼ 2 km s −1 Mpc −1 , sufficient to reliably resolve the current tension between local and cosmological measurements of H0.

Velocity correction for Hubble constant measurements from standard sirens

“…Although averaging over large GW samples can lead to an unbiased estimate of H 0 , the absence of a peculiar velocity correction will increase the error budget on H 0 due to the additional variance from the peculiar velocity contribution. In such a case, it's necessary to have a larger number of GW samples of N gw to beat the variance as N −1/2 gw (Nissanke et al 2010(Nissanke et al , 2013aChen et al 2018;Feeney et al 2019;Mortlock et al 2019). Incorporating an accurate correction for the peculiar velocity of the host of GW sources, we can achieve faster and more economically accurate, and also precise, measurements of H 0 .…”

“…Whether this discrepancy is associated with systematic or calibration errors in either of the data sets or whether it indicates new physics is currently a subject of intense debate. In this context, the spotlight has turned to standard sirens (Schutz 1986;Abbott et al 2017a), with binary neutron star mergers as an independent probe with the potential to reach the percent-level precision needed to validate the low redshift (z) determination of H 0 (Dalal et al 2006;Nissanke et al 2010Nissanke et al , 2013aChen et al 2018;Feeney et al 2019;Seto & Kyutoku 2018;Mortlock et al 2019). This potential crucially depends on whether the contamination from the peculiar velocity can be corrected at the required level of accuracy.…”

First Measurement of the Hubble Constant from a Dark Standard Siren using the Dark Energy Survey Galaxies and the LIGO/Virgo Binary–Black-hole Merger GW170814

“…The first standard siren-based H 0 measurement (Abbott et al 2017a) came with the discovery of the binary-neutron-star (BNS) merger GW170817 (Abbott et al 2017) and its associated electromagnetic counterpart (Arcavi et al 2017;Coulter et al 2017;LIGO Scientific Collaboration et al 2017;Lipunov et al 2017;Soares-Santos et al 2017;Tanvir et al 2017;Valenti et al 2017). Several studies have developed methodologies to infer cosmological parameters from standard sirens and establish their constraining power (Schutz 1986;Holz & Hughes 2005;MacLeod & Hogan 2008;Nissanke et al 2010Nissanke et al , 2013Del Pozzo 2012;Nishizawa 2017;Chen et al 2018;Feeney et al 2019;Mortlock et al 2018;Vitale & Chen 2018). Chen et al (2018) predicted that we will be able to constrain H 0 with 2% precision within 5 yr with standard sirens detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo, while Nair et al (2018) predicted a ∼7% measurement with just 25 binary-black-hole (BBH) events from the Einstein telescope.…”

Localizing merging black holes with sub-arcsecond precision using gravitational-wave lensing

“…Here we have assumed that the dominant correlation between luminosity distance and other parameters is the inclination, which is supported by several analyses detailing the luminosity distance-inclination degeneracy (e.g. (Mortlock et al 2019;Hotokezaka et al 2019)). Nevertheless, including all correlations could slightly improve our measurement accuracies.…”