Galaxy Halo Assembly Bias

今天观察到的大尺度结构需要一个额外的影响因素，而不是由弗里德曼-勒梅特-罗伯逊-沃克度量给出的同质和各向同性范式。早期宇宙中的量子扰动可以通过膨胀变成宏观的，在物质场中留下过密度的区域。星系形成的一个要求是，我们需要一个比我们今天观察到的“重子”物质所能提供的引力势大得多的引力势。这很自然地导致了一种说法，即无压物质反而推动了宇宙的膨胀和结构的增长。通过微扰理论，因果接触中的过密度线性增长，然而一些区域可以非线性增长，导致最终坍缩成晕。这些光晕被认为是由暗物质组成的，它们为星系等结构的生长提供了绝佳的环境，因为引力坍缩平衡了所含粒子的随机运动。小光晕形成较早，然后可以通过一系列分层合并而增长。然而，光晕的增长深深地依赖于环绕它们的宇宙网的更大的几何环境。宇宙网的区域可以被分类为一系列的空洞、细丝、片或结（例如Eardley et al. 2015, Joachimi et al. 2016），这取决于在引力坍缩中看到的维度数量。例如，可以观测到的星系团结在三维空间中坍缩，并产生强大的潮汐力，影响周围较小的光晕的生长。因此，可观测星系的特性被认为与它们周围的光晕环境和它们所处的几何环境有着内在的联系。然而，识别暗示晕的属性和历史的星系特征往往是微妙的，因此需要对数据丰富的调查进行仔细的统计分析。特别地，装配偏差对应于对于相同质量的光晕的理论；形成较早的光晕比形成较晚的光晕聚集得更强烈。这一点之前已经被发现，通过发现具有较低的恒星形成率的中心星系，因此更古老，通常比给定总恒星质量的活跃恒星形成的星系聚集更多（例如Wang et al. 2013）。由于暗物质在电磁上不可见这一明显的障碍，重建晕的过去需要多种创新方法的结合。当前（MaNGA (SDSS-IV)）和未来（DESI和Euclid）的调查保证了这种分析所需的数据丰富的框架。该项目的第一个目标是将单个星系组成部分（如恒星和气体）的运动特性与周围暗物质晕的运动特性联系起来。由于气体和恒星合并后弛豫时间尺度的差异，它们的旋转偏差可能可以作为光晕年龄的基础，从而进一步测试组装偏差。培训完成：STFC暑期学校科学辅导与示范：介绍评估与学术不端（科学）：介绍研究生研究员入门（所有学科）研究生研究员必备知识多样性工作场所在线培训模块2016年9月研究生培训代表培训正在进行/待完成：SUPA入门SUPA研究生院(20小时核心技能/ 40小时物理学习，包括：高级数据分析（第一学期）、观测课程（第二学期）)动漫大会及上海新生学校在特内里费岛泰德天文台望远镜培训之旅

The large scale structure observable today requires an additional influencing factor over the homogenous and isotropic paradigm given by the Friedmann-Lemaitre-Robertson-Walker metric. Quantum perturbations in the early Universe can become macroscopic through inflation, leaving regions of over-density in the matter field. A requirement of galaxy formation is that we need a far greater gravitational potential than can be given through the amount of 'baryonic' matter we observe today. This naturally leads to the suggestion that instead pressureless matter drives the Universe's expansion and structure growth. Over-densities in causal contact grow linearly through perturbation theory, however some regions can grow non-linearly leading to eventual collapse into halos. Assumed to be composed of dark matter, these halos provide an excellent environment for structure growth, such as galaxies, since the gravitational collapse balances the random motions of the contained particles. Small halos form earlier and then can grow through a series of hierarchical merging. Halo growth is however deeply dependent on the larger geometric environment of the cosmic web which encompasses them. Regions of the cosmic web can be classified as a series of voids, filaments, sheets or knots (e.g. Eardley et al. 2015, Joachimi et al. 2016) depending on the number of dimensions seen to be in gravitational collapse. Knots, observable as galaxy clusters, are collapsing in three dimensions and produce strong tidal forces affecting the growth of smaller surrounding halos, for example. The characteristic properties of observable galaxies therefore are thought to be inherently linked to both their surrounding halo environment and the geometric environment they reside in. Identifying galaxy features which imply the attributes and history of the halo, however, are often subtle and hence require careful statistical analysis of data-rich surveys. In particular assembly bias corresponds to the theory that for halos of the same mass; earlier forming halos are more strongly clustered than their later forming counterparts. This previously has been detected through finding that central galaxies with a lower specific star formation rate, and therefore are older, typically cluster more than those with active star formation for a given total stellar mass (e.g. Wang et al. 2013). Due to the obvious obstacle of dark matter being electromagnetically invisible, reconstructing a halo's past requires a combination of innovative approaches.Current (MaNGA (SDSS-IV)) and future (DESI and Euclid) surveys promise the data-rich framework that such analyses require. The first aim of this project is to link the kinematic properties of individual galaxy components, such as stars and gas, to the kinematics of the surrounding dark matter halo. Due to the difference in post-merger relaxation timescales of gas and stars, their rotational misalignment may be able to act as a primer on halo age and therefore a further test of assembly bias. Training Completed:STFC Summer SchoolTutoring and Demonstrating in the Sciences: An introductionAssessment & Academic Misconduct (Science): An introductionPostgraduate Researcher Induction (all disciplines)Postgraduate Researcher EssentialsDiversity in the Workplace Online Training Module September 2016Class Rep training for PG repsTraining in process / to be completed:SUPA Induction SUPA Graduate School (20 hours core skills / 40 hours physics learning including: Advanced Data Analysis (Semester 1), Observing Course (Semester 2)) MaNGA conference and new student school in ShanghaiTelescope training trip at Teide Observatory, Tenerife