NANOGrav 15年数据集中无可分辨源对超大质量黑洞双星系统的约束
Constraints on Supermassive Black Hole Binaries from the Lack of Resolvable Sources in the NANOGrav 15-yr Dataset
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中文总结 AI 辅助
利用NANOGrav 15年数据中未探测到连续波的上限，约束超大质量黑洞双星群体，发现其偏好较低质量源主导引力波背景，并打破质量与数量的简并。
中文摘要 AI 辅助
脉冲星计时阵列（PTAs）已发现引力波背景（GWB）的证据，与超大质量黑洞双星（SMBHBs）群体一致，但尚未解析出单个双星产生的连续波（CW）。我们基于NANOGrav 15年（NG15）数据，首次提出纳入PTA对连续波上限的SMBHB群体约束。使用半解析模型生成模拟群体，我们通过自由谱比较计算每个样本的GWB似然，并通过（1）将每个实现的最大连续波信噪比（S/N）映射到探测概率，以及（2）计算没有足够近的双星以至于NG15能够探测到的实现比例，来计算连续波未探测（nCW）似然。连续波未探测倾向于由许多较低质量源而非少数超大质量源主导GWB的群体。该信息与GWB振幅提供的信息互补，打破了复现观测谱所需双星质量与数量之间的简并。相对于仅GWB约束，联合后验倾向于更高的星系合并率、更低的$M_\mathrm{BH}$-$M_\mathrm{bulge}$离散度、更短的双星寿命以及更陡的小间距硬化。在S/N加权联合后验中，最可探测源的啁啾质量约为$10^{9.6} M_\odot$，光度距离约为1300 Mpc，频率约为6 nHz，而仅nCW约束则倾向于较低频率，与NG15 4 nHz候选源重合。如果连续波未探测持续，这些约束将进一步加强。
英文摘要
Pulsar timing arrays (PTAs) have found evidence of a gravitational wave background (GWB) consistent with a population of supermassive black hole binaries (SMBHBs), but have not yet resolved a continuous wave (CW) from an individual binary. We present the first SMBHB population constraints incorporating PTA upper limits on CWs, based on the NANOGrav 15-year (NG15) data. Using semi-analytic models to generate simulated populations, we calculate each sample's GWB likelihood by free spectral comparison and CW nondetection (nCW) likelihoods by (1) mapping each realization's highest CW signal-to-noise ratio (S/N) to a detection probability and (2) counting the fraction of realizations without a binary close enough that NG15 would have detected it. CW nondetection favors populations in which many lower-mass sources, rather than a few ultramassive ones, dominate the GWB. This information is complementary to that provided by the GWB amplitude, breaking the degeneracy between the masses and number of binaries required to reproduce the observed spectrum. Relative to GWB-only constraints, the joint posteriors favor higher galaxy merger rates, lower $M_\mathrm{BH}$-$M_\mathrm{bulge}$ scatter, shorter binary lifetimes, and steeper small-separation hardening. The most detectable sources in the S/N-weighted joint posterior have chirp masses $\sim 10^{9.6} M_\odot$, luminosity distances $\sim$1300 Mpc, and frequencies $\sim$6 nHz, while the nCW-only constraints favor lower frequencies, coinciding with the NG15 4 nHz candidate. These constraints will tighten if CW nondetection continues.
发表机构
- University of California, Berkeley（加州大学伯克利分校）
- University of Michigan（密歇根大学）
- University of Birmingham（伯明翰大学）
- University of Florida（佛罗里达大学）
- West Virginia University（西弗吉尼亚大学）
- University of Wisconsin-Milwaukee（威斯康星大学密尔沃基分校）
- University of North Carolina, Chapel Hill（北卡罗来纳大学教堂山分校）
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