Varstrometry for Off-nucleus and Dual Subkiloparsec Active Galactic Nuclei (VODKA): Investigating the Nature of SDSS J0823+2418 at z = 1.81, A Likely Lensed Quasar
Varstrometry for Off-nucleus and Dual Subkiloparsec Active Galactic Nuclei (VODKA): Investigating the Nature of SDSS J0823+2418 at z = 1.81, A Likely Lensed Quasar
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DOI：
10.3847/1538-4357/acf469
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发表时间：
2023-10
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通讯作者：
Arran C. Gross;Yu-Ching Chen;A. Foord;Xin Liu;Yue Shen;M. Oguri;A. Goulding;H. Hwang;N. Zakams
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作者：
Arran C. Gross;Yu-Ching Chen;A. Foord;Xin Liu;Yue Shen;M. Oguri;A. Goulding;H. Hwang;N. Zakams
在小的物理距离上的对偶类星体是星系合并的重要前兆阶段，最终导致两个超大质量黑洞的合并。从一个样本的双重和/或透镜类星体候选人发现使用盖亚数据中的天体测量抖动，我们提出了一个试点案例研究的最有前途的，但令人费解的候选人之一的双重类星体在宇宙中午（z = 1.8）。利用从X射线到射电的多波长成像和光谱学，我们测试了SDSS J 0823 +2418系统是否是两个独立的类星体，它们以0.0064的间距结合在一起，或者是一个被前景星系引力透镜的类星体。我们发现两个光源在光学、近红外（NIR）、紫外线和无线电中的通量比一致（1.25−1.45），因此光谱能量分布相似，表明存在强透镜效应。然而，射电光谱指数的差异，以及不断变化的X射线通量，暗示要么是一个具有几乎相同性质的双类星体，要么是基于透镜的时间滞后为2.3天，伴随着内在的变化。我们发现，与透镜质量模型的相对近红外位置和大小的两个类星体和边缘检测到的中央星系是一致的强透镜。斯隆数字巡天光谱档案同样建议通过镁ii吸收线前景吸收。我们的结论是，SDSS J 0823 +2418可能是一个透镜类星体，因此VODKA样本包含这些透镜系统的人口（可能高达50%）以及双类星体。
Dual quasars at small physical separations are an important precursor phase of galaxy mergers, ultimately leading to the coalescence of the two supermassive black holes. Starting from a sample of dual and/or lensed quasar candidates discovered using astrometric jitter in Gaia data, we present a pilot case study of one of the most promising yet puzzling candidate dual quasars at cosmic noon (z ∼ 1.8). Using multiwavelength imaging and spectroscopy from X-ray to radio, we test whether the SDSS J0823+2418 system is two individual quasars in a bound pair at separation ∼0.″64, or instead a single quasar being gravitationally lensed by a foreground galaxy. We find consistent flux ratios (∼1.25−1.45) between the two sources in optical, near-IR (NIR), UV, and radio, and thus similar spectral energy distributions, suggesting a strong-lensing scenario. However, differences in the radio spectral index, as well as changing X-ray fluxes, hint at either a dual quasar with otherwise nearly identical properties or perhaps lensing-based time lag of ∼3 days paired with intrinsic variability. We find with lens mass modeling that the relative NIR positions and magnitudes of the two quasars and a marginally detected central galaxy are consistent with strong lensing. Archival Sloan Digital Sky Survey spectra likewise suggest a foreground absorber via Mg ii absorption lines. We conclude that SDSS J0823+2418 is likely a lensed quasar, and therefore that the VODKA sample contains a population of these lensed systems (perhaps as high as 50%) as well as dual quasars.