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Abstract

We investigate the impact of uncertainty in the metallicity-specific star
formation rate over cosmic time on predictions of the rates and masses of
double compact object mergers observable through gravitational waves. We find
that this uncertainty can change the predicted detectable merger rate by more
than an order of magnitude, comparable to contributions from uncertain physical
assumptions regarding binary evolution, such as mass transfer efficiency or
supernova kicks. We statistically compare the results produced by the COMPAS
population synthesis suite against a catalog of gravitational-wave detections
from the first two Advanced LIGO and Virgo observing runs. We find that the
rate and chirp mass of observed binary black hole mergers can be well matched
under our default evolutionary model with a star formation metallicity spread
of $0.39$ dex around a mean metallicity $\left<Z\right>$ that scales with
redshift $z$ as $\left<Z\right>=0.035 \times 10^{-0.23 z}$, assuming a star
formation rate of $0.01 \times (1+z)^{2.77} / (1+((1+z)/2.9)^{4.7}) \,
\rm{M}_\odot$ Mpc$^{-3}$ yr$^{-1}$. Intriguingly, this default model predicts
that 80\% of the approximately one binary black hole merger per day that will
be detectable at design sensitivity will have formed through isolated binary
evolution with only dynamically stable mass transfer, i.e., without
experiencing a common-envelope event.