Galaxy groups provide the means for a great diversity of studies that contribute to a better understanding of the structure of the universe on a large scale and allow the properties of galaxies to be linked to those of the host halos. However, the identification of galaxy systems is a challenging task and therefore it is necessary to improve the techniques involved as much as possible. In view of the large present and forthcoming galaxy catalogues, we propose, implement, and evaluate an algorithm that combines the two most popular techniques used to identify galaxy systems. The algorithm can be easily applied to any spectroscopic galaxy catalogue, but here we demonstrate its use on the Sloan Digital Sky Survey. Assuming that a galaxy group is a gravitationally bounded system that has at least one bright galaxy, we begin by identifying groups with a Friends-Of-Friends algorithm adapted to fit this definition. In view of the shortcomings of this method, particularly the lack of ability to identify low-number groups, and consequently the inability to study the occupation of halos throughout the mass range, we improve it by adding a halo-based procedure. To assess the performance, we construct a mock catalogue from a semi-analytical model to compare the groups identified using our method with those obtained from the simulation. The comparison of groups extracted using our method with those of a mock catalogue shows that the proposed algorithm provides excellent results. The modifications introduced to the Friends-Of-Friends algorithm in the first part of the procedure to fit the adopted group definition gave reliable groups. Furthermore, the incorporation of the halo-based method reduces the interlopers while more accurately reproducing the number of galaxies per group. As a specific application, we use the algorithm to extract groups from the Sloan Digital Sky Survey.
In this paper we investigate how the halo mass function evolves with redshift, based on a suite of very large (with N_p = 3072^3 - 6000^3 particles) cosmological N-body simulations. Our halo catalogue data spans a redshift range of z = 0-30, allowing us to probe the mass function from the dark ages to the present. We utilise both the Friends-of-Friends (FOF) and Spherical Overdensity (SO) halofinding methods to directly compare the mass function derived using these commonly used halo definitions. The mass function from SO haloes exhibits a clear evolution with redshift, especially during the r…
CNN+FoF: application of deep learning to the identification of dark matter haloes
Ludwig-Maximilians-Universität München（慕尼黑大学）；Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理研究所）；Instituto de Astronomía Teórica y Experimental, UNC–CONICET（科尔多瓦国立大学-阿根廷国家科学研究委员会理论及实验天体物理研究所）；Observatorio Astronómico de Córdoba, UNC（科尔多瓦天文台）
New leaves of the tree: percolation analysis for cosmic web with discrete points
渗透分析长期以来一直被用来量化宇宙网络的连通性。以前的工作大多是基于网格上的密度场。通过平滑到场，我们丢失了关于星系属性的信息，如形状或光度。缺乏数学模型也限制了我们对渗流分析的理解。为了克服这些困难，我们研究了基于离散点的渗流分析。使用朋友圈（FoF）算法，我们生成S-bb关系，最大连接群（S）的分数质量和FoF连接长度（bb）之间。我们提出了一个新的模型，概率云集群扩展理论（PCCET）的S-bb关系与关联函数。我们表明，S-BB关系反映了组合的所有顺序的关联函数。利用N体模拟，我们发现S-bb关系对红移失真和观测不完全性是鲁棒的。从Bolshoi模拟，与Halo Abbreviation匹配（HAM），我们已经产生了一个模拟星系目录。投影的两点关联函数与观测值的匹配良好。然而，将模拟目录与SDSS DR 12的最新星系目录进行比较，我们发现它们的S-bb关系存在显着差异。这表明模拟星系表不能准确地保留比两点关联函数更高阶的关联函数，从而揭示了HAM方法的局限性。S-bb关系作为一种新的测量方法，具有适用范围广、计算速度快、抗红移失真和不完备性等优点，并且包含了关联函数的所有阶次信息。
CWTHF: Subhalo Identification with Continuous Wavelet Transform
Center for Theoretical Physics, College of Physics, Jilin University（吉林大学物理学院理论物理中心）；Key Laboratory of Material Simulation Methods & Software of Ministry of Education, College of Physics, Jilin University（吉林大学物理学院教育部材料模拟方法与软件重点实验室）；Center for High Energy Physics, Peking University（北京大学高能物理研究中心）
jFoF: GPU Cluster Finding with Gradient Propagation
Kavli IPMU (WPI), UTIAS, The University of Tokyo（东京大学）；Center for Data-Driven Discovery, Kavli IPMU (WPI), UTIAS, The University of Tokyo（东京大学）；Lawrence Berkeley National Lab（劳伦斯伯克利国家实验室）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所）；Department of Astrophysical Sciences, Peyton Hall, Princeton University（普林斯顿大学）
ELUCID -- Exploring the Local Universe with the reConstructed Initial Density field. II: Reconstruction diagnostics, applied to numerical halo catalogs
The First Systematic Survey of Stellar Halos in High-Inclination Galaxies Reveals Unusually Quiescent Merger Histories of Nearby Galaxies
University of Science and Technology of China（中国科学技术大学）；Shanghai Jiao Tong University（上海交通大学）；University of Oxford（牛津大学）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉各拉纳大学）
First Identification of a CMB Lensing Signal Produced by $1.5$ Million Galaxies at $z\sim$4: Constraints on Matter Density Fluctuations at High Redshift
