Revealing the ${\chi }_{\mathrm{eff}}$-$q$ Correlation among Coalescing Binary Black Holes and Tentative Evidence for AGN-driven Hierarchical Mergers

Abstract

The origin of the correlation between the effective spins (${\chi }_{\mathrm{eff}}$) and mass ratios ($q$) of LIGO-Virgo-KAGRA's binary black holes (BBHs) is still an open question. Motivated by the recent identification of two subpopulations of the BBHs, in this work we investigate the potential ${\chi }_{\mathrm{eff}}-q$ correlation for each subpopulation. Surprisingly, the ${\chi }_{\mathrm{eff}}$-$q$ correlation {either significantly weakens or disappears} for the low-mass subpopulation if we introduce a second ${\chi }_{\mathrm{eff}}$ distribution for the high-mass subpopulation, which likely originates from hierarchical mergers. {This suggests that the ${\chi }_{\mathrm{eff}}$-$q$ correlation in the overall population can be explained by the superposition of two distinct subpopulations.} {We find Bayesian evidence strongly favoring two separate ${\chi }_{\mathrm{eff}}$ distributions over a single mass-ratio-dependent distribution, with Bayes factors $\ln \mathcal{B}>4.2$.} The first subpopulation has a narrow ${\chi }_{\mathrm{eff}}$ distribution peaking at $\sim 0.05$, whose primary-mass function {showing a rapid decline beyond} $\sim 40M_{\odot }$, in agreement with first-generation BBHs. The second ${\chi }_{\mathrm{eff}}$ distribution is broad and peaks at ${\mu }_{\chi ,2}\sim 0.4$, aligning with predictions for hierarchical mergers in active galactic nucleus (AGN) disks. {However, we cannot exclude negative ${\chi }_{\mathrm{eff}}$values in the second subpopulation, suggesting hierarchical mergers might occur both in AGN disks and stellar clusters. Furthermore, the inferred second ${\chi }_{\mathrm{eff}}$ distribution might alternatively arise from other formation channels, such as stable mass transfer or chemically homogeneous evolution, if not interpreted as hierarchical mergers.}

arXiv comment14 pages, 9 figures, ApJ Accepted

References in corpus (32)

• Cosmic Star Formation History
• GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs
• GWTC-2: Compact Binary Coalescences Observed by LIGO and Virgo During the First Half of the Third Observing Run
• GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run
• Merging binary black holes formed through chemically homogeneous evolution in short-period stellar binaries
• Extracting distribution parameters from multiple uncertain observations with selection biases
• Mind the gap: The location of the lower edge of the pair instability supernovae black hole mass gap
• One Channel to Rule Them All? Constraining the Origins of Binary Black Holes using Multiple Formation Pathways
• Setting the cornerstone for the IMRPhenomX family of models for gravitational waves from compact binaries: The dominant harmonic for non-precessing quasi-circular black holes
• On stellar-mass black hole mergers in AGN disks detectable with LIGO
• Hierarchical Black Hole Mergers in Active Galactic Nuclei
• Hierarchical mergers of stellar-mass black holes and their gravitational-wave signatures
• The origin of spin in binary black holes: Predicting the distributions of the main observables of Advanced LIGO
• Measuring the binary black hole mass spectrum with an astrophysically motivated parameterization
• The impact of mass-transfer physics on the observable properties of field binary black hole populations
• Accuracy Requirements for Empirically-Measured Selection Functions
• The Emergence of Structure in the Binary Black Hole Mass Distribution
• Exploring Features in the Binary Black Hole Population
• Coalescing black hole binaries from globular clusters: mass distributions and comparison to gravitational wave data from GWTC-3
• Ain't No Mountain High Enough: Semi-Parametric Modeling of LIGO-Virgos Binary Black Hole Mass Distribution
• Resolving the Stellar-Collapse and Hierarchical-Merger origins of the Coalescing Black Holes
• LIGO--Virgo correlations between mass ratio and effective inspiral spin: testing the active galactic nuclei channel
• Potential Subpopulations and Assembling Tendency of the Merging Black Holes
• Limits on hierarchical black hole mergers from the most negative ${\chi }_{\mathrm{eff}}$ systems
• Evidence for a correlation between binary black hole mass ratio and black-hole spins
• Black-hole mergers in disklike environments could explain the observed $q$-${\chi }_{\mathrm{eff}}$ correlation
• Unequal-mass, highly-spinning binary black hole mergers in the stable mass transfer formation channel
• Avoiding a Cluster Catastrophe: Retention Efficiency and the Binary Black Hole Mass Spectrum
• Divergence in mass ratio distributions between low-mass and high-mass coalescing binary black holes
• Spin Doctors: How to diagnose a hierarchical merger origin
• Exploring field-evolution and dynamical-capture coalescing binary black holes in GWTC-3
• The origin channels of hierarchical binary black hole mergers in the LIGO-Virgo-KAGRA O1, O2, and O3 runs

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