Unveiling the link between galaxies and large-scale structures in the Sloan Digital Sky Survey

红移测量揭示了星系追踪复杂的结构网络，其中突出的高密度特征，如星团和细丝，与大片几乎空旷的区域交织在一起。理论模型和模拟表明，由早期宇宙中产生的微小密度扰动的引力不稳定性自然产生了与观测到的宇宙网性质相似的“宇宙网”。长期以来，对宇宙网的定量观测研究一直是不可能的，因为星系红移调查覆盖的体积太小，或者采样率太低，无法自动和客观地检测大规模结构。然而，最新一代调查在绘制低红移宇宙方面取得的革命性进展填补了这一空白。另一方面，我们现在处于未知领域，因为缺乏识别大型结构所需的工具。基于过去数值模拟和大样本观测的经验，我们建议：1.发展一种通用而简单的方法来识别高采样率大星系星表中的大尺度结构，如空洞、壁、细丝和团块；2.将该方法应用于斯隆数字巡天(SDSS)，以便识别不同大尺度环境中的星系；3.研究SDSS星系的基本性质是否以及如何与大尺度环境相关，特别是收集沿细丝向星系吸积冷气的证据；4.量化SDSS星系与其宿主大尺度结构之间的排列。作为回报，这项研究计划将1。开启了迄今为止以两点和三点统计测量为主的星系团研究的新篇章；2.将星系的小尺度物理与大尺度结构的组装联系起来，从而架起了星系形成和宇宙学的桥梁；3.澄清了星系自旋和形状的起源及其与底层大尺度结构的关系；4.了解困扰宇宙切变调查的内在星系-星系和星系-切变排列的起源。

Redshift surveys have revealed that galaxies trace a complex network of structures where prominent high-density features as clusters and filaments are interweaved with large nearly empty regions. Theoretical models and simulations show that a “cosmic web”, qualitatively similar to the observed one, is naturally produced by the gravitational instability of tiny density perturbations produced in the early universe. A quantitative observational study of the cosmic web has long been impossible because galaxy redshift surveys either covered too small a volume or had too a low sampling rate to allow an automatic and objective detection of large-scale structures. However, the revolutionary progress in mapping the low-redshift universe enabled by the latest generation of surveys has filled this gap. On the other hand, we are now in uncharted territory, because the tools necessary to identify the large-scale structures are lacking. Building on our past experience with numerical simulations and large observational samples, we thus propose to:1. develop a general and simple method to identify large-scale structures such as voids, walls, filaments and clumps in large galaxy catalogs with high sampling rate;2. apply the method to the Sloan Digital Sky Survey (SDSS) so that to identify galaxies in different large-scale environments;3. investigate if and how the fundamental properties of SDSS galaxies correlate with the large-scale environment and, in particular, collect evidence for cold-gas accretion onto galaxies along filaments;4. quantify the alignment between SDSS galaxies and their host large-scale structures.In return, this research programme will1. open a new chapter in the study of galaxy clustering so far dominated by measurements of 2-point and 3-point statistics;2. connect the small-scale physics of galaxies with the assembly of the large-scale structure, thus bridging galaxy formation and cosmology;3. clarify the origin of galactic spins and shapes and their relation to the underlying large-scale structure;4. understand the origin of intrinsic galaxy-galaxy and galaxy-shear alignments that plague cosmic-shear surveys.