# The effect of the metallicity-specific star formation history on double compact object mergers

## TL;DR

This paper examines how uncertainties in metallicity-specific star formation history affect predictions of double compact object merger rates and masses, highlighting the importance of metallicity evolution in gravitational wave observations.

## Contribution

It introduces a model incorporating metallicity evolution and compares it with gravitational wave data, revealing the significant impact of metallicity uncertainties on merger predictions.

## Key findings

- Uncertainty in metallicity-specific star formation rate can alter merger rate predictions by over an order of magnitude.
- The default model matches observed binary black hole merger rates and masses.
- 80% of detectable binary black hole mergers are predicted to form through isolated binary evolution without a common-envelope event.

## 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.