LIGO Document P2100185-v6

Constraints on the cosmic expansion history from GWTC-3

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05 Nov 2021, 09:08
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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