CASSOWARY 20：一个宽间隔爱因斯坦十字架的X射线光谱仪鉴定
CASSOWARY 20: a Wide Separation Einstein Cross Identified with the X-shooter Spectrograph
摘要：
我们使用最近在欧洲南方天文台甚大望远镜上使用的三臂光学-红外光谱仪X-shooter获得的光谱来确认CASSOWARY候选CSWA 20的引力透镜性质。该系统由一个红移z（abs）= 0.741的明亮红色星系组成，具有非常高的速度色散σ（透镜）= 500 km/s，它将一个z（em）= 1.433的蓝色恒星形成星系透镜成四个图像，平均间隔约为6角秒。这个来源与z = 2-3的紫外选择星系有许多共同的性质：它以每年25个太阳质量的速度形成恒星，金属量约为1/4太阳，并且在图像平面上显示出两个相隔0.4角秒的组成部分的星云发射，可能表明合并。看来，银河系内的前景星际物质已经从我们观察星暴的视线中撤离，给出了它的恒星和H II区域的未熄灭的视图。CSWA 20，其巨大的透镜星系产生一个高放大率的本征发光背景星系，是一个有前途的目标，为未来的研究在各种波长。
英文摘要：
We have used spectra obtained with X-shooter, the triple arm optical-infrared spectrograph recently commissioned on the Very Large Telescope of the European Southern Observatory, to confirm the gravitational lens nature of the CASSOWARY candidate CSWA 20. This system consists of a luminous red galaxy at redshift z(abs) = 0.741, with a very high velocity dispersion sigma(lens) = 500 km/s, which lenses a blue star-forming galaxy at z(em) = 1.433 into four images with mean separation of about 6 arcseconds. The source shares many of its properties with those of UV-selected galaxies z = 2-3: it is forming stars at a rate of 25 solar masses per year, has a metallicity of about 1/4 solar, and shows nebular emission from two components separated by 0.4 arcseconds in the image plane, possibly indicating a merger. It appears that foreground interstellar material within the galaxy has been evacuated from the sight-line along which we observe the starburst, giving an unextinguished view of its stars and H II regions. CSWA 20, with its massive lensing galaxy producing a high magnification of an intrinsically luminous background galaxy, is a promising target for future studies at a variety of wavelengths.
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