The Formation of Cosmic Structure: 2011-2016

在过去的二十年里，我们看到了宇宙几何和物质含量的标准模型的出现，以及宇宙中所有结构的起源和演化。根据这个“λ - cdm”模型，我们生活在一个具有平坦几何形状的宇宙中，其中至少三分之二的质量-能量现在以暗能量场的形式存在，这导致宇宙以不断增加的速度膨胀。大约四分之一是暗物质，很可能是一种新的弱相互作用的基本粒子，尚未在地球上直接探测到。只有大约5%是普通物质或重子物质，其中只有大约十分之一存在于今天的恒星中，其余大部分存在于星系间气体中。在宇宙大爆炸的最初瞬间，宇宙质量密度中的量子涨落为结构埋下了种子。这些声波在近乎均匀的原始等离子体中产生微弱的声波，在宇宙大爆炸遗留下来的热量上留下了可观察到的印记，当时宇宙只有40万年的历史。通过对宇宙微波背景辐射的成像，这些微小的涟漪逐渐形成了我们今天所看到的丰富结构。正是这种从近乎均匀的原始汤到由星系、星系团和更大结构组成的宇宙网络的转变，才是这项应用的重点。重力，主要是由于暗物质，放大了微小的原始涟漪，导致暗物质和气体块停止随着宇宙膨胀而坍缩，形成今天的宇宙结构。这个过程很复杂，但可以通过计算机模拟计算出来。对于给定的一系列关于早期宇宙中不均匀性的产生、暗物质的身份和宇宙学参数的值的假设，模拟可以跟踪宇宙结构的形成历史，相当详细地跟踪暗物质、气体和恒星的演化。超级计算机模拟是我们研究项目的很大一部分，其中大部分工作都是在“处女座联盟”中进行的，这是一个由英国领导的国际合作组织，通常被认为是该领域的世界领导者。在过去的25年里，处女座联盟和前体合作在定义现代物理宇宙学方法和将Lambda-CDM建立为标准模型方面发挥了核心作用。我们的计划有六个相互关联的主题：(1)银河系晕，(2)河外气体的物理，(3)星系形成的模拟，(4)宇宙黎明和再电离，(5)星系和活动星系核的多波长建模，(6)千兆秒宇宙。我们的研究有三大目标。首先是了解宇宙中结构的形成，从星系和类星体到超星系团，通过这一点，建立暗物质和暗能量的本质，并在尚未经过测试的制度下探索Lambda-CDM模型。第二个目标是在理论和观测之间架起一座桥梁。模拟是最好的，通常也是唯一的，从宇宙学和天体物理学理论中形成可观测预测的方法。我们的第三个目标是通过分析星系调查和我们的模拟来提取关于真实宇宙的宇宙学信息。我们是国际Pan-STARRS1项目的一部分，这是新一代全景光度调查的第一个项目，目标是惊人的科学气息，从潜在的“杀手”小行星到宇宙的大规模结构。我们领导了12个重点项目之一的Pan-STARRS1，研究宇宙大尺度结构。执行像我们这样的复杂性和规模的模拟是大多数团队无法达到的。我们认为，提供对这些独特数据集的访问是我们的专业职责，我们计划的一个重要组成部分是模拟数据和衍生品的管理和出版。

The past twenty years have seen the emergence of a standard model for the geometry and material content of our Universe, as well as for the origin and evolution of all structure within it. According to this ``Lambda-CDM'' model, we live in a universe with a flat geometry where at least two thirds of all mass-energy is now in the form of a dark energy field which is causing the universe to expand at an ever increasing rate. About a quarter is dark matter, most probably a new weakly interacting elementary particle yet to be detected directly on Earth. Only about 5 percent is ordinary, or baryonic, matter of which only about a tenth is in stars today and the rest resides mostly in intergalactic gas. Structure was seeded by quantum fluctuations imprinted in the mass density of the universe at the earliest instants of the Big Bang. These produced weak sound waves in the near-uniform primordial plasma that left observable imprints on the heat left over from the Big Bang, emitted when the universe was only 400,000 years old. These tiny ripples, mapped by imaging the cosmic microwave background radiation, grew into the full richness of structure we see around us today. It is this transformation from a near-uniform primordial soup to a cosmic web of galaxies, clusters and larger structures that is the focus of this application. Gravity, mostly due to dark matter, amplifies the tiny primordial ripples, causing lumps of dark matter and gas to stop expanding with the universe and collapse to form today's cosmic structures. This process is complex, but can be calculated by computer simulation. For a given a set of assumptions regarding the generation of inhomogeneities in the early universe, the identity of the dark matter, and the values of the cosmological parameters, simulations can follow the formation history of cosmic structure, tracking the evolution of dark matter, gas and stars, in considerable detail. Supercomputer simulations are a large part of our research programme and much of this work takes place within the `Virgo consortium', a UK-led international collaboration which is generally recognized as the world leader in the subject. Over the past 25 years, the Virgo consortium and precursor collaborations have played a central role in defining the modern approach to physical cosmology and establishing Lambda-CDM as the standard model. Our programme has six interrelated themes: (1) the Milky Way halo, (2) the physics of extragalactic gas, (3) simulations of galaxy formation, (4) the cosmic dawn and reionization, (5) multi-wavelength modelling of galaxies and active galactic nuclei and (6) the Gigaparsec universe. Our research has three broad goals. The first is to understand the formation of structures in the Universe, from galaxies and quasars to superclusters and, through this, establish the nature of the dark matter and the dark energy, and explore the Lambda-CDM model in as yet untested regimes. The second goal is to provide a bridge between theory and observations. Simulations are the best, often the only, means to formulate observable predictions from cosmological and astrophysical theory. Our third goal is to extract cosmological information about the real universe by analysing galaxy surveys in tandem with our simulations. We are part of the international Pan-STARRS1 project, the first of a new generation of panoramic photometric surveys which targets an astonishing breath of science, from potential `killer' asteroids, to the large-scale structure of the Universe. We are leading one of the 12 key Pan-STARRS1 projects, on the cosmic large-scale structure. Performing simulations of the complexity and size or ours is beyond the reach of most groups. We regard it as our professional duty to provide access to these unique datasets and an important component of our programme is the curation and publication of simulation data and derivatives.