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Abstract Gravitational-wave detectors are starting to reveal the redshift evolution of the binary black hole (BBH) merger rate,RBBH(z). We make predictions forRBBH(z) as a function of black hole mass for systems originating from isolated binaries. To this end, we investigate correlations between the delay time and black hole mass by means of the suite of binary population synthesis simulations,COMPAS. We distinguish two channels: the common envelope (CE), and the stable Roche-lobe overflow (RLOF) channel, characterized by whether the system has experienced a common envelope or not. We find that the CE channel preferentially produces BHs with masses below about 30M⊙and short delay times (tdelay≲ 1 Gyr), while the stable RLOF channel primarily forms systems with BH masses above 30M⊙and long delay times (tdelay≳ 1 Gyr). We provide a new fit for the metallicity-dependent specific star formation rate density based on the Illustris TNG simulations, and use this to convert the delay time distributions into a prediction ofRBBH(z). This leads to a distinct redshift evolution ofRBBH(z) for high and low primary BH masses. We furthermore find that, at high redshift,RBBH(z) is dominated by the CE channel, while at low redshift, it contains a large contribution (∼40%) from the stable RLOF channel. Our results predict that, for increasing redshifts, BBHs with component masses above 30M⊙will become increasingly scarce relative to less massive BBH systems. Evidence of this distinct evolution ofRBBH(z) for different BH masses can be tested with future detectors.
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This content will become publicly available on September 11, 2026
Searching for Binary Black Hole Subpopulations in Gravitational-wave Data Using Binned Gaussian Processes
Abstract Astrophysically motivated population models for binary black hole (BBH) observables are often insufficient to capture the imprints of multiple formation channels. This is mainly due to the strongly parametrized nature of such investigations. Using a nonparametric model for the joint population-level distributions of BBH component masses and effective inspiral spins, we find hints of multiple subpopulations in the third gravitational-wave transient catalog. The higher (more positive) spin subpopulation is found to have a mass spectrum without any feature at in the 30–40M⊙range, which is consistent with the predictions of isolated stellar binary evolution, simulations for which place the pileup due to pulsational pair-instability supernovae near 50M⊙or higher. The other subpopulation with effective spins closer to zero shows a feature at 30–40M⊙and is consistent with BBHs formed dynamically in globular clusters, which are expected to peak around 30M⊙. We also compute merger rates for these two subpopulations and find that they are consistent with the theoretical predictions of the corresponding formation channels. We validate our results by checking their robustness against variations of several model configurations and by analyzing large simulated catalogs with the same model.
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- Award ID(s):
- 2207728
- PAR ID:
- 10637358
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 991
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 17
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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