用哈勃太空望远镜研究A520的暗核：谜团加深
A Study of the Dark Core in A520 with Hubble Space Telescope: The Mystery Deepens
摘要：
我们提出了一个哈勃太空望远镜/宽视场行星相机2弱透镜研究A520，其中以前的地面数据分析表明存在一个黑暗的质量浓度。我们映射复杂的质量结构，更详细地利用超过三个因素的增加源星系的数量密度可用于透镜分析。与X射线气体峰重合的“暗核”，但不与任何恒星光度峰重合，现在检测到的意义超过10 sigma。在NE-SW方向上延伸的~ 1.5Mpc的次级结构也清晰可见。从表面上看，暗物质、团内介质和星系亮度的质心之间的比较与在其他具有类似几何配置的合并星系团中观察到的结果不一致。到目前为止，最显著的反例可能是子弹星团，它显示出与A520一样明显的弓形激波特征，但在X射线气体周围没有明显的弱透镜质量集中。根据最新的数据，我们考虑了几种可能的解释，这些解释可能导致在A520中检测到这种特殊的功能。然而，我们的结论是，这些情景中没有一个可以单独挑选出来作为这个难题的明确解释。
英文摘要：
We present a Hubble Space Telescope/Wide Field Planetary Camera 2 weak-lensing study of A520, where a previous analysis of ground-based data suggested the presence of a dark mass concentration. We map the complex mass structure in much greater detail leveraging more than a factor of three increase in the number density of source galaxies available for lensing analysis. The "dark core" that is coincident with the X-ray gas peak, but not with any stellar luminosity peak is now detected with more than 10 sigma significance. The ~1.5 Mpc filamentary structure elongated in the NE-SW direction is also clearly visible. Taken at face value, the comparison among the centroids of dark matter, intracluster medium, and galaxy luminosity is at odds with what has been observed in other merging clusters with a similar geometric configuration. To date, the most remarkable counter-example might be the Bullet Cluster, which shows a distinct bow-shock feature as in A520, but no significant weak-lensing mass concentration around the X-ray gas. With the most up-to-date data, we consider several possible explanations that might lead to the detection of this peculiar feature in A520. However, we conclude that none of these scenarios can be singled out yet as the definite explanation for this puzzle.
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