<tt>McFACTS</tt> . II. Mass Ratio–Effective Spin Relationship of Black Hole Mergers in the Active Galactic Nucleus Channel

Abstract We use the Monte Carlo For AGN Channel Testing and Simulation ( McFACTS ; https://www.github.com/mcfacts/mcfacts ) code to study the effect of active galactic nucleus (AGN) disk and nuclear star cluster (NSC) model parameters on predicted mass distributions for LIGO–Virgo–KAGRA compact binaries forming in AGN disks. The assumptions we vary include the black hole (BH) initial mass function (IMF), disk model, disk size, disk lifetime, NSC model, and the prograde-to-retrograde fraction of newly formed BH binaries. Broadly, we find that dense, moderately short-lived AGN disks are preferred for producing a ( q , χ eff ) anticorrelation like those identified from existing gravitational-wave observations. Additionally, a BH IMF (IMF ∝ M −2 ) is preferred over a more top-heavy IMF ( M −1 ). To produce results consistent with observations, the preferred fraction of prograde to retrograde is >90%.