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arXiv 1209.2143astro-ph.CO
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暗峰与质量缺失:合并星系团Abell 520的弱透镜质量重建

On Dark Peaks and Missing Mass: A Weak Lensing Mass Reconstruction of the Merging Cluster System Abell 520

Douglas Clowe, Maxim Markevitch, Marusa Bradac, Anthony H. Gonzalez, Sun Mi Chung, Richard Massey, Dennis Zaritsky

摘要:

星系团的合并是独特的,因为它们有能力直接探测和限制暗物质的自相互作用截面。对几个正在合并的星系团的详细观测表明,星系团内的气体会被冲压压力从暗物质和星系密度的质心处移开,而后者的成分在空间上是重合的,这与无碰撞的暗物质是一致的。这被用来确定暗物质粒子自相互作用截面的上限为1 cm ^2/g。星系团Abell 520被认为是一个可能的例外。我们重新审视A520,展示新的HST ACS马赛克图像和麦哲伦图像集。我们进行了详细的弱透镜分析,并表明,弱透镜质量测量和形态的核心星系填充结构大多是在良好的协议与以前的工作。然而,有一个显着的区别-我们没有检测到先前声称的“暗核心”,它包含多余的质量,在X射线等离子体的位置没有显着的星系过密度。这个峰值被认为是暗物质的大的自相互作用截面的指示(至少比子弹星系团观测确定的上限0.7 cm ^2/g大~5 sigma)。我们没有发现这样的迹象,而是发现A520的质量分布,减去X射线等离子体质量后,与星系团星系的光度分布吻合得很好。我们的结论是,A520没有显示出与无碰撞暗物质假设相矛盾的证据。

英文摘要:

Merging clusters of galaxies are unique in their power to directly probe and place limits on the self-interaction cross-section of dark matter. Detailed observations of several merging clusters have shown the intracluster gas to be displaced from the centroids of dark matter and galaxy density by ram pressure, while the latter components are spatially coincident, consistent with collisionless dark matter. This has been used to place upper limits on the dark matter particle self-inteaction cross-section of order 1 cm^2/g. The cluster Abell 520 has been seen as a possible exception. We revisit A520 presenting new HST ACS mosaic images and a Magellan image set. We perform a detailed weak lensing analysis and show that the weak lensing mass measurements and morphologies of the core galaxy-filled structures are mostly in good agreement with previous works. There is however one significant difference -- we do not detect the previously claimed "dark core" that contains excess mass with no significant galaxy overdensity at the location of the X-ray plasma. This peak has been suggested to be indicative of a large self-interaction cross-section for dark matter (at least ~5 sigma larger than the upper limit of 0.7 cm^2/g determined by observations of the Bullet Cluster). We find no such indication and instead find that the mass distribution of A520, after subtraction of the X-ray plasma mass, is in good agreement with the luminosity distribution of the cluster galaxies. We conclude that A520 shows no evidence to contradict the collisionless dark matter scenario.

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