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arXiv 2201.08358astro-ph.GA
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来自星系形成半解析模型的紧致群-- III：类希克森星表的纯粹性和完备性

Compact groups from semi-analytical models of galaxy formation -- III: purity and completeness of Hickson-like catalogues

Antonela Taverna, Eugenia Diaz-Gimenez, Ariel Zandivarez, Gary Mamon

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13 pages, 5 figures, 5 tables, accepted for publication in MNRAS
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摘要：

许多孤立的致密星系群（CG）的星表都是使用希克森的标准来识别孤立的致密星系系统，至少有三到四个星系的星等和红移一致。但目前还不清楚在何种程度上的CG目录是完整和可靠的，相对于3D真正孤立的，密集的群体。使用五种不同的半解析模型的星系形成（SAMs），我们确定孤立的致密集团在三维真实空间中，包含至少三个星系。然后，我们建立模拟的红移空间星系目录，并运行一个希克森式的CG查找器。我们发现红移空间中的类希克森算法在恢复至少3个星系的3D CG方面较差，纯度为$\sim 10\%$，完整性为$\sim 22\%$。在虚假系统的$\sim 90\%$中，典型的$60\%$是不符合三维隔离标准的致密结构，而其余的$40\%$是沿着视线的星系的偶然排列，几乎所有的星系都在规则的星系群中，与用于分析的SAM有一些变化。换句话说，虽然只有$10\%$的CG是孤立的密集组，如预期的那样，一半是嵌入较大组内的密集结构，三分之一是较大组内的偶然对齐。提取的CG样本的低完整性主要是由于选择标准的通量限制。我们的研究结果表明，一个新的观测算法，以确定在红移空间中的紧凑群体，需要获得密集的孤立星系系统。

英文摘要：

Many catalogues of isolated compact groups of galaxies (CGs) have been extracted using Hickson's criteria to identify isolated, dense systems of galaxies, with at least three or four galaxies concordant in magnitude and redshift. But is not clear to what extent the catalogues of CGs are complete and reliable, relative to 3D truly isolated, dense groups. Using five different semi-analytical models of galaxy formation (SAMs), we identify isolated dense groups in 3D real space, containing at least three galaxies. We then build mock redshift space galaxy catalogues and run a Hickson-like CG finder. We find that the Hickson-like algorithm in redshift space is poor at recovering 3D CGs of at least 3 galaxies, with a purity of $\sim 10\%$ and a completeness of $\sim 22\%$. Among the $\sim 90\%$ of spurious systems, typically $60\%$ are dense structures that failed the 3D isolation criteria, while the remaining $40\%$ are chance alignments of galaxies along the line of sight, nearly all of which are within regular groups, with some variation with the SAM used for the analysis. In other words, while only $10\%$ of CGs are isolated dense groups, as intended, half are dense structures embedded within larger groups, and one-third are chance alignments within larger groups. The low completeness of the extracted CG sample is mainly due to the flux limits of the selection criteria. Our results suggest that a new observational algorithm to identify compact groups in redshift space is required to obtain dense isolated galaxy systems.

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