局域宇宙中的紧致群在哪里？
Where are compact groups in the local Universe?
摘要：
这项工作的目的是从观测和半分析的角度对宇宙中紧致群的位置进行统计分析。我们使用了从2微米全天巡天中提取的速度过滤紧致群样本进行分析。我们还使用了一个新的样本的星系群中确定的2M++星系红移目录作为示踪剂的大尺度结构。我们定义了一个程序来搜索在红移空间中的紧凑的群体，可以被认为是嵌入在其他过密系统，并应用此标准的几种可能的组合不同的紧凑和星系群的子样本。我们还进行了类似的分析，在2M++模拟星系目录从千年运行模拟我加上半分析模型的星系形成确定的模拟紧凑和星系群。我们观察到，只有$\sim27\%$的紧群可以被认为是嵌入在更大的超稠密系统，也就是说，大多数的紧群更有可能是孤立系。嵌入式紧凑组显示统计上较小的尺寸和更明亮的表面亮度比非嵌入式系统。没有证据表明嵌入的紧凑群体更有可能居住在具有给定维里质量或特定动力学状态的星系群中。当使用模拟致密体和星系群进行分析时，我们发现了非常相似的结果。基于半解析研究，我们预测嵌入紧群的$70\%$可能是三维物理稠密系统。最后，真实的空间信息使我们能够揭示紧凑和星系群之间的三维最小距离分布的双峰行为。在比较先验不同环境中星系的性质时，应仔细考虑致密群的位置。
英文摘要：
The purpose of this work is to perform a statistical analysis of the location of compact groups in the Universe from observational and semi-analytical points of view. We used the velocity-filtered compact group sample extracted from the Two Micron All Sky Survey for our analysis. We also used a new sample of galaxy groups identified in the 2M++ galaxy redshift catalogue as tracers of the large-scale structure. We defined a procedure to search in redshift space for compact groups that can be considered embedded in other overdense systems and applied this criterion to several possible combinations of different compact and galaxy group subsamples. We also performed similar analyses for simulated compact and galaxy groups identified in a 2M++ mock galaxy catalogue constructed from the Millennium Run Simulation I plus a semi-analytical model of galaxy formation. We observed that only $\sim27\%$ of the compact groups can be considered to be embedded in larger overdense systems, that is, most of the compact groups are more likely to be isolated systems. The embedded compact groups show statistically smaller sizes and brighter surface brightnesses than non-embedded systems. No evidence was found that embedded compact groups are more likely to inhabit galaxy groups with a given virial mass or with a particular dynamical state. We found very similar results when the analysis was performed using mock compact and galaxy groups. Based on the semi-analytical studies, we predict that $70\%$ of the embedded compact groups probably are 3D physically dense systems. Finally, real space information allowed us to reveal the bimodal behaviour of the distribution of 3D minimum distances between compact and galaxy groups. The location of compact groups should be carefully taken into account when comparing properties of galaxies in environments that are a priori different.
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