第一个爱因斯坦环MG 1131+0456的红移
A Redshift for the First Einstein Ring, MG 1131+0456
摘要：
MG 1131+0456是一个射电选择引力透镜，也是第一个已知的爱因斯坦环。该系统发现于1988年，由一个明亮的射电源成像成一个环和两个紧凑的，平坦的频谱成分，间隔为2.1角秒。环的光学亮度较暗（R = 23.3），在近红外和中红外波段（K = 17.8; W2 = 13.4）急剧上升。该系统在随后的几年中得到了深入的研究，包括高分辨率无线电成像，无线电监测以及哈勃和凯克的近红外成像。透镜星系的z（lens）= 0.844。然而，到目前为止，还没有关于透镜源的光谱红移的报道。利用1997年的Keck档案数据，我们报告了在5438埃处的单个窄发射线的稳健检测，我们将其与z（源）= 1.849的2型类星体的CIII] 1909联系起来。支持这种红移的证据来自CIV 1549和HeII 1640的较弱发射，这是典型的2型类星体，以及在档案近红外凯克光谱中缺乏发射线。我们还首次介绍了MG 1131+0456的第1周期钱德拉观测，它清楚地分解为两个点源，其组合通量为~ 1 e-13 erg/cm 2/s，最佳拟合柱密度为~ 3e 22/cm 2。我们提出了一种新的方法来识别候选透镜活动星系核从低分辨率的X射线调查，如eROSITA的目标源，具有令人不安的高X射线光度鉴于其中红外光度。
英文摘要：
MG 1131+0456 is a radio-selected gravitational lens, and is the first known Einstein ring. Discovered in 1988, the system consists of a bright radio source imaged into a ring and two compact, flat-spectrum components separated by 2.1 arcsec. The ring is optically faint (R = 23.3), rising steeply into the near- and mid-infrared (K = 17.8; W2 = 13.4). The system has been intensively studied in the intervening years, including high-resolution radio imaging, radio monitoring, and near-infrared imaging with Hubble and Keck. The lensing galaxy is at z(lens) = 0.844. However, to date, no spectroscopic redshift had been reported for the lensed source. Using archival Keck data from 1997, we report the robust detection of a single narrow emission line at 5438 Angstroms, which we associate with CIII] 1909 from a type-2 quasar at z(source) = 1.849. Support for this redshift identification comes from weaker emission associated with CIV 1549 and HeII 1640, typical of type-2 quasars, as well as the lack of emission lines in archival near-infrared Keck spectroscopy. We also present, for the first time, Cycle 1 Chandra observations of MG 1131+0456, which clearly resolves into two point sources with a combined flux of ~1e-13 erg/cm2/s and a best-fit column density of ~3e22 /cm2. We suggest a new method to identify candidate lensed active galactic nuclei from low-resolution X-ray surveys such as eROSITA by targeting sources that have anomalously high X-ray luminosity given their mid-infrared luminosity.
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