Abstract
Abstract We introduce a semiparametric model for the primary mass distribution of binary black holes (BBHs) observed with gravitational waves (GWs) that applies a cubic-spline perturbation to a power law. We apply this model to the 46 BBHs included in the second gravitational-wave transient catalog (GWTC-2). The spline perturbation model recovers a consistent primary mass distribution with previous results, corroborating the existence of a peak at 35 M ⊙ (>97% credibility) found with the Powerlaw+Peak model. The peak could be the result of pulsational pair-instability supernovae. The spline perturbation model finds potential signs of additional features in the primary mass distribution at lower masses similar to those previously reported by Tiwari and Fairhurst. However, with fluctuations due to small-number statistics, the simpler Powerlaw+Peak and BrokenPowerlaw models are both still perfectly consistent with observations. Our semiparametric approach serves as a way to bridge the gap between parametric and nonparametric models to more accurately measure the BBH mass distribution. With larger catalogs we will be able to use this model to resolve possible additional features that could be used to perform cosmological measurements and will build on our understanding of BBH formation, stellar evolution, and nuclear astrophysics.
Highlights
The LIGO-Virgo Collaboration’s second catalog of compact object mergers has shown that the universe is teeming with colliding compact objects with a variety of masses and spins (Abbott et al 2016)
We introduce a semi-parametric model for the primary mass distribution of binary black holes (BBHs) observed with gravitational waves (GWs) that applies a cubic-spline perturbation to a power law
Accurate estimation of the BBH mass distribution is paramount to getting accurate estimates of merger rates, the GW stochastic background, and false alarm rates for potential new triggers
Summary
The LIGO-Virgo Collaboration’s second catalog of compact object mergers has shown that the universe is teeming with colliding compact objects with a variety of masses and spins (Abbott et al 2016). The presence of these high mass component black holes could point towards there being a contribution to the observed population of BBHs detected by LIGO/Virgo, that formed in a way that avoids PI These formation possibilities include hierarchical mergers in dense stellar environments, relativistic accretion onto heavy BHs in active galactic nuclei disks, isolated binary evolution of low-metallicity Population II stars, or even the presence of new physics beyond the standard model (Rodriguez et al 2019; Doctor et al 2020; Kimball et al 2020a,b; Doctor et al 2021; McKernan et al 2020; Belczynski 2020; Croon et al 2020; Mapelli et al 2020).
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