arXiv 1503.027562015-03-10astro-ph.COastro-ph.GA

结构形成对星系团中心金属丰度的影响？

Are the Effects of Structure Formation Seen in the Central Metallicity of Galaxy Clusters?

Tamer Y. Elkholy, Mark W. Bautz, Claude R. Canizares

备注：: Accepted in ApJ, March 9, 2015
DOI：: 10.1088/0004-637X/805/1/3

摘要：

钱德拉观测到的46个邻近星系团的样本被分析，以产生径向密度，温度，熵和金属丰度分布，以及其他形态测量。熵配置文件计算到更大的径向范围比以前的钱德拉集群样本分析。我们发现，在内部0.15 R500测量的铁的质量分数显示了更大的分散在整个样品的低质量的集群，比它的样品的高质量的集群。我们将这一发现解释为大星系团中比小星系团中混合更多的晕的结果，这导致大星系团中金属含量的平均化，从而导致高质量星系团的金属丰度分散度较小。这种解释支持了这样一种观点，即合并晕中的低熵、富含金属的气体到达了星系团的中心，这解释了核心塌陷超新星产物金属丰度峰值的观测，并在流体动力学模拟中看到。为了支持我们的解释，这些合并晕中的气体必须到达星系团的中心，而不会在外部区域混合。另一方面，金属丰度分散度不随团簇外部区域的质量而变化，这表明大多数外部金属来自金属丰度水平更均匀的来源，例如在预富集期间。我们还测量了低质量团簇中的金属含量和它们的团簇内介质（ICM）在形态上受到干扰的程度之间的相关性，如通过质心位移测量的。这表明了另一种解释的金属丰度分布在低质量的集群，从而在低质量集群的中心的金属丰度提高诱导作为一个过渡状态，在合并过程中的大宽度。

英文摘要：

A sample of 46 nearby clusters observed with Chandra is analyzed to produce radial density, temperature, entropy and metallicity profiles, as well as other morphological measurements. The entropy profiles are computed to larger radial extents than in previous Chandra cluster sample analyses. We find that the iron mass fraction measured in the inner 0.15 R500 shows a larger dispersion across the sample of low-mass clusters, than it does for the sample of high-mass clusters. We interpret this finding as the result of the mixing of more haloes in large clusters than in small clusters, which leads to an averaging of the metal content in the large clusters, and thus less dispersion of metallicity for high-mass clusters. This interpretation lends support to the idea that the low-entropy, metal-rich gas of merging haloes reaches clusters' centers, which explains observations of Core-Collapse Supernova products metallicity peaks, and which is seen in hydrodynamical simulations. The gas in these merging haloes would have to reach the centers of clusters without mixing in the outer regions, in order to support our interpretation. On the other hand, metallicity dispersion does not change with mass in the outer regions of clusters, suggesting that most of the outer metals come from a source with a more uniform metallicity level, such as during pre-enrichment. We also measure a correlation between the metal content in low-mass clusters and the degree to which their Intra-Cluster Medium (ICM) is morphologically disturbed, as measured by centroid shift. This suggests an alternative interpretation of the large width of the metallicity distribution in low-mass clusters, whereby a metallicity boost in the center of low-mass clusters is induced as a transitional state, during mergers.

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