Galactic Archaeology: Unveiling the History of the Milky Way

一项惊人的考古挖掘正在进行中--RAVE，径向速度实验，正在利用太阳附近10万颗恒星的空间运动(已经是之前历史积累的几倍)来绕回时间之箭，这是社区长期目标的第一步，该目标是艰苦地逐星重建我们银河系的组装历史。解开星系形成的基本物理，无论是遥远的“远场”还是本地的“近场”，是STFC和英国天文学界的最高科学优先事项之一，也是STFC拥有既得利益的数十亿英镑技术投资背后的根本动机。横穿夜空的那道光--即所谓的银河系--是如何产生的？由数千亿颗恒星组成，年龄跨度超过100亿年，每一颗恒星的运动轨迹都非常不同，恒星之间的化学丰度模式不同，其化学丰度模式的系数超过一百万，颜色和亮度甚至截然不同。乍一看，似乎几乎不可能拼凑出像我们银河系这样的盘状(或螺旋)星系的形成历史。更令人望而生畏的是，试图将今天这个高度复杂的系统与可见宇宙边缘看到的遥远的光斑与哈勃太空望远镜和其他由STFC支持的天文台(如双子座和欧洲南方天文台)联系起来。在非凡的RAVE数据集的推动下，以及欧洲航天局的GAIA任务和双子星/斯巴鲁WFMOS项目等下一代银河系考古实验的前景，我们开发了先进的计算技术，能够追踪银河系等星系的生命周期，从遥远的“斑点”到今天我们周围数十亿颗恒星的结构。我们开发了一个快速而灵活的软件包，它几乎包括了推动银河系形成和演化的所有重要物理过程；虽然有许多代码可用于模拟纯恒星类系统(所谓的“无碰撞”系统)的运动学，但今天市场上很少有包括相关气体物理的并行处理的代码。我们的软件包不仅包括重力的临界效应，还包括气体动力学、气体加热(来自爆炸的恒星和奇异的超大质量黑洞)、气体冷却(来自星际原子过程)、恒星形成、垂死恒星的化学浓缩以及整个模拟星系中恒星群体的光度和颜色演变。关于我们银河系的起源，我们已经看到了许多谜团：为什么它周围的卫星‘积木’带有看起来与我们的银河系完全不同的化学指纹？为什么这些卫星出现在银河系周围的特殊轨道上，而不是随机定向？是什么造成了我们原本平坦的银河系圆盘上的张开翘曲？在银河系外围观察到的相对年轻的星系团的起源是什么，这些星系团带有化学指纹，同样看起来与周围的恒星一点也不像？除了几种化学元素外，为什么我们斑驳而斑驳的银河晕在化学上是如此的均匀？RAVE、WFMOS和GAIA等数据集为大量恒星提供了前所未有的空间、运动学和化学数据。在STFC的支持下，我们的团队将挖掘嵌入这些新数据集中的银河系化石记录(或指导它们的潜在开发，如WFMOS和GAIA)，以了解盘星系及其暗物质晕的详细3D形状，并进一步深入了解吸积事件在塑造这些性质中的作用。

An astonishing archaeological dig is underway - RAVE, the RAdial Velocity Experiment, is using the space motions of one hundred thousand stars (already several times the number previously accumulated throughout history) in the vicinity of the Sun to wind time's arrow back, the first step in a long-term community goal of making a painstaking star-by-star reconstruction of the assembly history of our Milky Way. Disentangling the underlying physics of galaxy formation, whether it be the distant 'far-field' or the local 'near-field' is one of the highest scientific priorities for both STFC and the UK astronomy community, and a fundamental motivation behind several billion-pound technological investments in which STFC has a vested interest. How did the swath of light which cuts across the night sky - the so-called Milky Way - originate? Comprised of hundreds of billions of stars, with ages spanning more than ten billion years, each moving on very different trajectories, with chemical abundance patterns varying by factors of more than a million from star-to-star, and colours and luminosities even more dramatically different, at first glance it would appear all but impossible to piece together the formation history of a disk (or spiral) galaxy like our own Milky Way. Even more daunting would apppear to be attempts to link this highly complex system today with distant 'blobs' of light seen at the edge of the visible Universe with facilities such as the Hubble Space Telescope and other STFC-supported observatories such as Gemini and the European Southern Observatory. Motivated by the extraordinary RAVE dataset, and the promise of proposed next-generation galactic archaeology experiments such as the European Space Agency's GAIA mission and the Gemini/Subaru WFMOS Project, we have developed sophisticated computational techniques capable of tracing the life cycle of galaxies such as the Milky Way, from distant 'blob' to the multi-billion star structure surrounding us today. We have developed a fast and flexible software package which includes virtually all of the important physical processes which drive the formation and evolution of galactic systems; while many codes are available for simulating the kinematics of purely stellar-like systems (so-called 'collisionless' systems), there are very few on the market today which include a parallel treatment of the relevant gas physics. Our software packages include the critical effects of not only gravity, but also gas dynamics, gas heating (from exploding stars and exotic supermassive black holes), gas cooling (from interstellar atomic processes), star formation, chemical enrichment from dying stars, and the luminosity and colour evolution of the stellar populations throughout the simulated galaxy. We are already presented with a number of mysteries regarding the origin of our Milky Way: why do its surrounding satellite 'building blocks' bear chemical fingerprints which look nothing like our Galaxy? why do these satellites appear in special orbits around the Galaxy, as opposed to random orientations? what is responsible for the flared warp in our otherwise flat Milky Way disk? what is the origin of the relatively young clusters observed in the outskirts of our Galaxy, clusters with chemical fingerprints which, again, look nothing like the stars around them? why is our mottled and patchy galactic halo otherwise so homogeneous chemically, save for just a few chemical elements? Datasets such as RAVE, WFMOS, and GAIA provide unprecedented spatial, kinematic, and chemical, data for enormous numbers of stars. With the support of STFC, our team will mine the fossil record of the Milky Way embedded in these new datasets (or guide their potential exploitation, as in the case of WFMOS and GAIA), in order to understand the detailed 3d shape of disk galaxies and their dark matter halos, and gain further insight into the role of accretion events in shaping these properties.