离核和双亚千秒差距AGN（VODKA）变容测量：哈勃太空望远镜发现双类星体
Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA): Hubble Space Telescope Discovers Double Quasars
摘要：
$\sim$ kpc尺度的对偶超大质量黑洞（Dual supermassive black hole，SMBH）是SMBH并合的母体，对理解星系并合中大质量黑洞的配对和动力学演化具有重要作用。由于严格的分辨率要求和这些小分离对的明显稀有性，对这一种群的观测限制很少，在$z>1$的$<10$ kpc分离处几乎没有确认的双SMBH。在这里，我们提出了一个试点搜索的结果kpc规模的双类星体选择与盖亚数据发布2（DR2）天体测量和后续的哈勃太空望远镜（HST）宽视场相机3双波段（F475W和F814W）快照成像。我们的目标是类星体主要选择与varstrometry技术，即，光质心抖动引起的异步变化，从两个成员在一个未解决的类星体对，补充子arcsec对已经解决了盖亚DR2。我们发现，在变容测量选择的类星体（盖亚DR 2中未解析）中，HST解析对的总体比例很高，即$\sim 30-50\%$，向高红移方向增加（$z>1.5$的$\sim 60-80\%$）。我们讨论的性质的43个解决的分角秒对HST和补充数据的基础上。这些对中的相当一部分（$\sim 40\%$）可能是物理类星体对或引力透镜类星体。我们还发现了一个三重类星体候选者和一个四重透镜类星体，这是最小的分离四重透镜。这些结果为改进高红移下$\sim$ kpc尺度双SMBH的变容测量选择和后续确认提供了重要的指导。
英文摘要：
Dual supermassive black holes (SMBHs) at $\sim$kpc scales are the progenitor population of SMBH mergers and play an important role in understanding the pairing and dynamical evolution of massive black holes in galaxy mergers. Because of the stringent resolution requirement and the apparent rareness of these small-separation pairs, there are scarce observational constraints on this population, with few confirmed dual SMBHs at $<10$kpc separations at $z>1$. Here we present results from a pilot search for kpc-scale dual quasars selected with Gaia Data release 2 (DR2) astrometry and followed up with Hubble Space Telescope (HST) Wide Field Camera 3 dual-band (F475W and F814W) snapshot imaging. Our targets are quasars primarily selected with the varstrometry technique, i.e., light centroid jitter caused by asynchronous variability from both members in an unresolved quasar pair, supplemented by sub-arcsec pairs already resolved by Gaia DR2. We find an overall high fraction of HST-resolved pairs among the varstrometry-selected quasars (unresolved in Gaia DR2), $\sim 30-50\%$, increasing toward high redshift ($\sim 60-80\%$ at $z>1.5$). We discuss the nature of the 43 resolved sub-arcsec pairs based on HST and supplementary data. A substantial fraction ($\sim 40\%$) of these pairs are likely physical quasar pairs or gravitationally lensed quasars. We also discover a triple quasar candidate and a quadruply lensed quasar, which is among the smallest-separation quadruple lenses. These results provide important guidelines to improve varstrometry selection and follow-up confirmation of $\sim$kpc-scale dual SMBHs at high redshift.
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