Kavli Affiliate: Daniel E. Holz
| First 5 Authors: Amanda M. Farah, Thomas A. Callister, Jose María Ezquiaga, Michael Zevin, Daniel E. Holz
| Summary:
Gravitational waves (GWs) from merging compact objects encode direct
information about the luminosity distance to the binary. When paired with a
redshift measurement, this enables standard-siren cosmology: a Hubble diagram
can be constructed to directly probe the Universe’s expansion. This can be done
in the absence of electromagnetic measurements as features in the mass
distribution of GW sources provide self-calibrating redshift measurements
without the need for a definite or probabilistic host galaxy association. This
“spectral siren” technique has thus far only been applied with simple
parametric representations of the mass distribution, and theoretical
predictions for features in the mass distribution are commonly presumed to be
fundamental to the measurement. However, the use of an inaccurate
representation leads to biases in the cosmological inference, an acute problem
given the current theoretical uncertainties in the population. Here, we
demonstrate that spectral sirens can accurately infer cosmological parameters
without prior assumptions for the shape of the mass distribution. We apply a
flexible, non-parametric model for the mass distribution of compact binaries to
a simulated catalog of 1,000 GW events, consistent with expectations for the
next LVK observing run. We find that, despite our model’s flexibility, both the
source mass model and cosmological parameters are correctly reconstructed. We
predict a $5.8%$ measurement of $H_0$, keeping all other cosmological
parameters fixed, and a $6.4%$ measurement of $H(z=0.9)$ when fitting for
multiple cosmological parameters ($1sigma$ uncertainties). This
astrophysically-agnostic spectral siren technique will be essential to arrive
at precise and unbiased cosmological constraints from GW source populations.
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