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Dual quasars are expected to be common in the hierarchical structure formation paradigm. Despite their significance comma no confirmed dual quasar is known with <10 kpc separations at 1<z<3 comma in stark contrast to theoretical expectations. We propose STIS (G750L) slit spectroscopy for 14 double-core quasars to systematically discover close dual or lensed SMBHs at redshifts 1<z<3 for the first time. Our sample probes a new regime at higher redshifts and smaller merger separations than previous work - crucial for understanding the significance of mergers in triggering quasar activity in the cosmic d_commahigh noond_comma. Our targets are selected using the new astrometric techniquedoublePoint when two close-by AGN vary stochastically comma their combined light centroid shifts comma which is detectable by Gaia. Follow-up HST imaging of Gaia-selected targets has uncovered double-cored morphology with nuclear separations of virgul0.3d_comma-0.6d_comma. The proposed STIS spectra will reject interlopers such as chance superpositions with stars-galaxies to unambiguously confirm the targets as dual or lensed quasars. The results will provide empirical constraints on the merger rate of supermassive black holes and therefore on the stochastic gravitational wave background from binary supermassive black holes.

在分层结构形成范式（hierarchical structure formation paradigm）中，双类星体（dual quasars）应普遍存在。尽管其科学意义重大，但目前尚未在红移1<z<3的区间内发现分离度小于10千秒差距（kpc）的确认双类星体，这与理论预期形成鲜明反差。我们提议对14个双核类星体开展STIS（G750L）狭缝光谱观测，以期首次在红移1<z<3区间内系统性地发现近距离双超大质量黑洞（supermassive black holes, SMBHs）或引力透镜类星体。相较于此前的研究工作，本样本探索了更高红移、更小并合分离度的全新参数区间——这对理解宇宙正午（cosmic high noon）时期并合事件触发类星体活动的重要性至关重要。我们的目标源通过新型天体测量技术筛选：当两个近距离活动星系核（Active Galactic Nucleus, AGN）发生随机光度变化时，其复合光心会产生偏移，该效应可被盖亚（Gaia）卫星探测到。对盖亚筛选出的目标源开展的后续哈勃空间望远镜（Hubble Space Telescope, HST）成像观测，已发现核分离度介于0.3~0.6千秒差距之间的双核形态。本次拟开展的STIS光谱观测将剔除诸如恒星、星系偶然叠加这类干扰源，从而明确确认目标源为双类星体或引力透镜类星体。本研究结果将为超大质量黑洞并合率提供经验约束，进而为双超大质量黑洞产生的随机引力波背景（stochastic gravitational wave background）提供观测依据。