AI 中文总结
本研究基于IllustrisTNG模拟，发现结合$d_\text{off}$与$\triangle m_{12}$可有效指示星系群和团的弛豫性，提出的选择标准能构建匹配弛豫晕的HMF，还揭示了弛豫晕占比的红移演化规律。
AI 中文摘要
背景：星系群和星系团被广泛用于探测宇宙网演化与宇宙学研究，前提是假设它们处于弛豫状态。目的：我们确定最亮晕星系（BHG）的性质，这些性质可用于预测动力学弛豫主晕的最可能样本，本研究结合了深入研究的星系团与较少分析的星系群。方法：分析基于IllustrisTNG模拟数据，考虑了多个受观测驱动的参数，包括BHG相对于宿主系统势阱的偏移量（$d_\text{off}$）、相对于r波段光度中心的偏移量（$d_\text{lum}$）、最亮与第二亮星系的间距（$d_{12}$），以及两者的r波段星等差（$\triangle m_{12}$）。主要分析在红移$z=0$处进行，额外研究了直至$z=1$的晕弛豫性红移演化。将这些可观测代理用于构建晕质量函数（HMF），并与理论方法中常用三维信息定义的弛豫样本的HMF进行比较。结果：发现$d_\text{off}$与$\triangle m_{12}$是星系群和星系团弛豫性的有效指示物，尤其当两者结合使用时效果更佳。$d_\text{off}<0.05~R_{200}$且$\triangle m_{12}>1.6$星等的选择标准可使构建的HMF与弛豫晕群体的HMF高度匹配。这些标准可应用于$z\backsim0.2$以内、质量范围$\text M_{200}\backsim10^{12.5}\text M_\text{\textodot}$（$\text M_\text{*, BHG}\backsim10^{10.9}\text M_\text{\textodot}$）的观测，涵盖该质量范围内的星系群与星系团。在$z=0$时，该质量范围内15%-23%的系统被视为完全弛豫；弛豫晕占比随红移增加至$z\backsim0.4$而下降，之后下降速度大幅减缓。
英文摘要
Context. Galaxy groups and clusters are widely used to probe the evolution of the cosmic web and cosmology, while assuming that they are relaxed. Aims. We identify the properties of the brightest halo galaxies (BHGs) that can be used to predict the most likely sample of dynamically relaxed host halos. Our work combines thoroughly studied galaxy clusters with less frequently analysed groups. Methods. Our analysis was based on data from the IllustrisTNG simulations. We considered several observationally motivated parameters, including the offset of the BHG from the potential well of the host system ($d_\text{off}$) and from the r-band luminosity centre ($d_\text{lum}$), the distance between the brightest and second-brightest galaxies ($d_{12}$), and the r-band magnitude gap between them ($Δm_{12}$). The primary analysis was performed at redshift $z=0$, with an additional investigation of the redshift evolution of halo relaxation up to $z=1$. The observable proxies were applied to construct a halo mass function (HMF), which was then compared to the HMF of the relaxed sample defined from 3D information commonly used in theoretical approaches. Results. We find that $d_\text{off}$ and $Δm_{12}$ are effective indicators of group and cluster relaxation, particularly when used in combination. The selection criteria of $d_\text{off}<0.05~R_{200}$ and $Δm_{12}>1.6$ mag allowed us to reproduce an HMF that closely matches that of the relaxed halo population. These criteria can be applied to observations up to $z\sim0.2$ within a mass range $\text M_{200}\geq10^{12.5}\text M_\odot$ ($\text M_\text{*, BHG}\gtrsim10^{10.9}\text M_\odot$), including groups and clusters in the selection. In this mass range, $15-23\%$ of the systems are considered fully relaxed at $z=0$. The fraction of relaxed haloes decreases with redshift up to $z\sim0.4$, after which the decrease is far slower.
Comments12 pages, 18 figures. Accepted for publication in A&A
DOI：10.1051/0004-6361/202660522
