# Constraints on the cosmic expansion history from GWTC-3

Document #:
LIGO-P2100185-v6
Document type:
P - Publications
Other Versions:
 LIGO-P2100185-v5 05 Nov 2021, 09:08
Abstract:
We use 47 gravitational-wave sources from the Third LIGO-Virgo-KAGRA Gravitational-Wave Transient Catalog (GWTC-3) to estimate the Hubble parameter $$H(z)$$, including its current value, the Hubble constant $$H_0$$. Each gravitational-wave (GW) signal provides the luminosity distance to the source and we estimate the corresponding redshift using two methods: the redshifted masses and a galaxy catalog. Using the binary black hole (BBH) redshifted masses, we simultaneously infer the source mass distribution and $$H(z)$$. The source mass distribution displays a peak around $$34\, {\rm M_\odot}$$, followed by a drop-off. Assuming this mass scale does not evolve with redshift results in a $$H(z)$$ measurement, yielding $$H_0=68^{+13}_{-7} {\rm km\,s^{-1}\,Mpc^{-1}}$$ ($$68\%$$ credible interval) when combined with the $$H_0$$ measurement from GW170817 and its electromagnetic counterpart. This represents an improvement of 13% with respect to the $$H_0$$ estimate from GWTC-1. The second method associates each GW event with its probable host galaxy in the catalog GLADE+, statistically marginalizing over the redshifts of each event's potential hosts. Assuming a fixed BBH population, we estimate a value of $$H_0=68^{+8}_{-6} {\rm km\,s^{-1}\,Mpc^{-1}}$$ with the galaxy catalog method, an improvement of 41% with respect to our GWTC-1 result and 20% with respect to recent $$H_0$$ studies using GWTC-2 events. However, we show that this result is strongly impacted by assumptions about the BBH source mass distribution; the only event which is not strongly impacted by such assumptions (and is thus informative about $$H_0$$) is the well-localized event GW190814.
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