The Search for Signatures of Supermassive Black Hole Binaries (and the Remnants of those Mergers) in the Time Domain

双超大质量黑洞（SMBHs）应该是大质量星系通过合并增长的必然结果，也是宇宙中最强的引力波源。然而，由于引力束缚的SMBHs轨道距离很小，观测到星系和黑洞的这一基本变化阶段的证据仍然很难找到。在这个计划中，提议者将利用理论上预测的SMBH双星的特征：由质量吸积率引起的天体亮度随时间的周期性变化，而质量吸积率与双星的轨道运动有关。假设星系合并率、类星体寿命和亮度变化的合理值的理论估计，预测最近完成的Pan-STARRS1中深巡天（PS1 MDS）具有探测大量周期类星体所需的面积（80平方度）、周期（3天）、基线（4.2年）和星等灵敏度，这些类星体处于由引力波引起的双星SMBHs轨道衰减阶段。在这个项目中，pi将分析所有10个PS1 MDS场，包括7000多个光度选择的类星体。此外，他们将利用即将到来的兹威基瞬变设施（ZTF）的广阔区域和出色的节奏，使用差分成像来搜索与宿主星系中心在空间上偏移的活动星系核，这可能表明SMBH合并残余的反冲。这两项搜索都将为大型综合巡天望远镜（LSST）的令人兴奋的能力提供基准研究，LSST将具有更大数量级的巡天能力。

Part 1Binary supermassive black holes (SMBHs) should be an inevitable consequence of the growth of massive galaxies through mergers, and the strongest source of gravitational waves in the universe. However, observational evidence for this fundamental phase of changes in galaxy and black hole has remained hard to find due to the small orbital separations of gravitationally bound SMBHs. In this program, the proposers will exploit a theoretically predicted signature of a SMBH binary: periodic changes of the object's brightness over time, caused by a mass accretion rate that is linked to the binary's orbital motion.Part 2Theoretical estimates assuming reasonable values for the galaxy merger rates, quasar lifetime, and brightness variations, predict that the recently completed Pan-STARRS1 Medium Deep Survey (PS1 MDS) has the area (80 square degrees), cadence (3 days), baseline (4.2 years), and magnitude sensitivity required to detect a significant number of periodic quasars during the phase of their binary SMBHs's orbital decay cause by gravity waves. In this project the PIs will analyze all 10 PS1 MDS fields, including over 7,000 photometrically-selected quasars. Furthermore, they will exploit the wide area and excellent cadence of the upcoming Zwicky Transient Facility (ZTF) to use difference imaging to search for active galactic nuclei spatially offset from their host galaxy center, potentially indicative of a recoiling SMBH merger remnant. Both searches will provide benchmark studies for the exciting capabilities of Large Synoptic Survey Telescope (LSST), which will have orders of magnitude larger survey power.