发表机构
GRAPPA Institute, University of Amsterdam; Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), University of Tokyo（阿姆斯特丹大学 GRAPPA 研究所; 东京大学 宇宙物理数学 Kavli 研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
提出无需并合树的半解析框架，直接积分N体重标定吸积核计算超大质量黑洞引力波背景，并用NANOGrav 15年数据推断，发现黑洞质量归一化偏高约0.31 dex。
AI 中文摘要
我们提出一个半解析框架，通过直接积分一个经N体重新标定的扩展Press-Schechter吸积核来计算超大质量黑洞（SMBH）双星产生的引力波背景（GWB），完全绕过了蒙特卡洛并合树。该计算无分辨率依赖且速度足够快，可直接对脉冲星计时数据进行采样，无需模拟器或预计算模型库。在暗物质晕吸积与黑洞双星形成之间，我们将卫星星系的模拟标定潮汐质量损失与钱德拉塞卡动力学摩擦连续耦合。低于一个尖锐且几乎与红移无关的质量比阈值ξ≃0.04的卫星星系，其被剥离的速度快于下沉速度，从而停滞：其拖曳力坍缩到恒星核上，38%的被吸积卫星星系在z=0时未发生并合。将该种群模型与每双星的恒星硬化转折及偏心谱相结合，我们直接对NANOGrav 15年Hellings-Downs相关自由谱进行五参数后验采样，排除了15.8 nHz频段，该频段的过量功率在随后的色噪声重新分析中被归因于脉冲星噪声。数据倾向于黑洞质量归一化比局部标定的黑洞-核球质量关系高+0.31^{+0.20}_{-0.23} dex，这与早期迹象一致，即纳赫兹背景相对于局部SMBH标定显得响亮，且对延迟模型、并合核、局部质量标定及其红移演化具有鲁棒性。该谱与偏心双星或致密恒星环境相容，但并不要求它们存在。
英文摘要
We present a semi-analytic framework that computes the gravitational-wave background (GWB) from supermassive black hole (SMBH) binaries by direct integration of an $N$-body-recalibrated extended Press-Schechter accretion kernel, bypassing Monte Carlo merger trees entirely. The calculation is resolution-free and fast enough to be sampled directly against pulsar-timing data with no emulator or precomputed model bank. Between halo accretion and black-hole binary formation, we couple the satellite's simulation-calibrated tidal mass loss continuously to Chandrasekhar dynamical friction. Satellites below a sharp, nearly redshift-independent mass-ratio threshold, $ξ\simeq 0.04$, are stripped faster than they sink and stall: their drag collapses onto the stellar core, and 38% of accreted satellites are unmerged by $z=0$. Combining this population model with per-binary stellar-hardening turnovers and eccentric spectra, we sample the five-parameter posterior directly against the NANOGrav 15 yr Hellings-Downs-correlated free spectrum, excluding the $15.8$ nHz bin, whose excess power a subsequent chromatic-noise reanalysis attributes to pulsar noise. The data prefer a black-hole mass normalization $+0.31^{+0.20}_{-0.23}$ dex above the locally calibrated black-hole-bulge mass relation, consistent with earlier indications that the nanohertz background is loud relative to local SMBH calibrations and robust to the delay model, merger kernel, local mass calibration, and its redshift evolution. The spectrum is compatible with, but does not require, eccentric binaries or dense stellar environments.
Comments20 pages, 7 figures
