Coherence of Supermassive Black Hole Binary Demographics with the nHz Stochastic Gravitational Wave Background

Katsunori Kusakabe; Yoshiyuki Inoue; Daisuke Toyouchi

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arXiv · 2510.10548

Coherence of Supermassive Black Hole Binary Demographics with the nHz Stochastic Gravitational Wave Background

Katsunori Kusakabe·Yoshiyuki Inoue·Daisuke Toyouchi

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Abstract

We present a refined estimation of the stochastic gravitational wave background (SGWB) based on observed dual active galactic nuclei (AGNs) together with AGN X-ray luminosity functions, in light of recent Pulsar Timing Array detections of an nHz SGWB. We identify a characteristic luminosity dependence in dual AGN fractions by compiling recent observational datasets, providing crucial constraints on supermassive black hole binary (SMBHB) populations. Our AGN-based model reproduces the current SGWB measurements within PTA observational uncertainties of $2 - 4 \sigma$ uncertainties, demonstrating consistency between electromagnetic and gravitational wave observations. These findings establish SMBHBs as the dominant source of the nHz gravitational wave signal, providing crucial insights into their demographics and evolution.

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Katsunori Kusakabe, Yoshiyuki Inoue, Daisuke Toyouchi. 2025-10-12. Coherence of Supermassive Black Hole Binary Demographics with the nHz Stochastic Gravitational Wave Background. https://arxiv.org/abs/2510.10548

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