Massive BH binaries as periodically variable AGN
Massive BH binaries as periodically variable AGN
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DOI：
10.1093/mnras/stz150
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发表时间：
2018-09
影响因子：
4.8
通讯作者：
L. Kelley;Z. Haiman;A. Sesana;L. Hernquist
中科院分区：
文献类型：
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作者：
L. Kelley;Z. Haiman;A. Sesana;L. Hernquist
预计在其母星系合并后形成的大质量黑洞（MBH）双星会产生引力波，脉冲星计时阵列可以在纳赫兹频率（年周期）检测到引力波。虽然在电磁观测中尚未发现经证实的紧凑MBH双星系统，但最近在活动星系核变化的光学调查中发现了大量候选系统。结合宇宙学、流体动力学模拟；全面的半解析二元合并模型；以及分析 AGN 光谱和变异性处方；我们计算了MBH双星作为周期性变化的活动星系核的预期电磁探测率。特别是，我们考虑两个独立的变化模型：（i）由于大轨道速度导致的多普勒增强，以及（ii）流体动力学变化，其中MBH吸积盘的燃料由伴星周期性调节。我们的模型预测，现有数据中应该存在并可区分大量 MBH 双星。特别是，我们的基准模型产生的预期值为 0.2 美元（多普勒）和 5 美元（流体动力学）双星在 CRTS 中可识别，而经过 5 年 LSST 观测后预计为 20 美元和 100 美元。大多数系统中的亮度变化太小而无法区分，但红移 $z \lesssim 0.6$ 处的 AGN 几乎 $1\%$ 可能存在于巨大的双星中。我们分析了可观测系统的预测二元参数及其选择偏差，并对我们的模型参数和不确定性进行了广泛的讨论。
Massive black-hole (MBH) binaries, which are expected to form following the merger of their parent galaxies, produce gravitational waves which will be detectable by Pulsar Timing Arrays at nanohertz frequencies (year periods). While no confirmed, compact MBH binary systems have been seen in electromagnetic observations, a large number of candidates have recently been identified in optical surveys of AGN variability. Using a combination of cosmological, hydrodynamic simulations; comprehensive, semi-analytic binary merger models; and analytic AGN spectra and variability prescriptions; we calculate the expected electromagnetic detection rates of MBH binaries as periodically variable AGN. In particular, we consider two independent variability models: (i) Doppler boosting due to large orbital velocities, and (ii) hydrodynamic variability in which the fueling of MBH accretion disks is periodically modulated by the companion. Our models predict that numerous MBH binaries should be present and distinguishable in the existing data. In particular, our fiducial models produce an expectation value of $0.2$ (Doppler) and $5$ (hydrodynamic) binaries to be identifiable in CRTS, while $20$ and $100$ are expected after five years of LSST observations. The brightness variations in most systems are too small to be distinguishable, but almost $1\%$ of AGN at redshifts $z \lesssim 0.6$ could be in massive binaries. We analyze the predicted binary parameters of observable systems and their selection biases, and include an extensive discussion of our model parameters and uncertainties.