Understanding and Tracing Dark Matter in the Local Universe

暗物质将我们在宇宙中大尺度上看到的可见结构结合在一起，提供了致密的“晕”，在其中形成了单个星系和星系团。然而，暗物质的基本性质仍然未知，建立它与粒子物理学标准模型的其他部分的关系仍然是宇宙学的首要任务。在大尺度上，暗物质的聚集是很好理解的，观测和理论预测相匹配。在小尺度上，我们的观测探测器要少得多，暗物质的行为更具争议性。新的和即将到来的调查承诺大大改善这种情况，对星系团和引力透镜进行更灵敏的测量。理论家面临的挑战是跟上，使预测足够准确，以便充分利用这些数据。这是我提出的研究计划的目标，其中包括三个主要组成部分。 第一个组成部分是了解暗物质晕如何通过反复合并而发展。我已经开始了一个模拟主要晕合并的程序，以了解晕的结构特性如何与它们的形成历史相关。下一步是将我们的发现应用于宇宙学模拟，并将结果转化为观测测试。我们还打算研究小合并，这决定了单个星系如何在群体和集群中演化。 第二个组成部分是通过定义微弱卫星星系的局部样本并将其与模拟进行比较，来追踪暗物质子结构并表征小尺度上星系形成的效率。银河系的矮卫星比最简单的理论模型预测的要少，这就是著名的“失踪卫星问题”。然而，在星系团中，情况却截然不同，矮星似乎很丰富。为了解决星系形成在哪里以及为什么逐渐减少，我们需要更大的卫星群样本，在广泛的环境中，以及理论预测。我的小组已经开发出测量卫星丰度的技术，并计划将其应用于即将进行的几次调查。 该计划的最后一部分是研究单个星系内部和周围的暗物质密度。理论预测，星系团内部区域的星系应该形成得更早，并且有更高的暗物质密度。我们最近在室女座星系团中测试了这一预测，并检测到密度随径向位置的显著梯度。这项技术提供了一个新的，直接估计的集合时代的个别星系。我们建议将其应用到其他附近的星系团，但也高红移样本的密度约束动力学或透镜。 总之，这些组成部分应该提供更丰富的理论理解晕和subhalos，新的工具来研究星系的形成，和更严格的限制暗物质的属性。

Dark matter binds together the visible structure we see on large scales in the Universe, providing the dense 'halos' within which individual galaxies and groups and clusters of galaxies form. The fundamental nature of dark matter remains unknown, however, and establishing its relation to the rest of the Standard Model of particle physics remains a top priority in cosmology. On large scales, the clustering of dark matter is well understood, and observations and theoretical predictions match. On small scales, we have far fewer observational probes, and the behaviour of dark matter is more controversial. New and forthcoming surveys promise to improve this situation dramatically, with much more sensitive measurements of galaxy clustering and gravitational lensing. The challenge for theorists is to keep up, making predictions accurate enough to allow a full use of this data. This is the goal of my proposed research program, which includes three main components. The first component is to understand how dark matter halos evolve as they grow through repeated mergers. I have started a program of simulations of major halo mergers, to understand how the structural properties of halos relate to their formation history. The next steps are to apply our findings to cosmological simulations and translate the results into observational tests. We also intend to study minor mergers, which determine how individual galaxies evolve in groups and clusters. The second component is to trace dark matter substructure and characterize the efficiency of galaxy formation on small scales, by defining local samples of faint satellite galaxies and comparing them to simulations. The Milky Way has fewer dwarf satellites than predicted by the simplest theoretical models, the famous 'missing satellite problem'. In galaxy clusters, however, the picture is quite different, and dwarfs seem abundant. To resolve where and why galaxy formation tapers off, we need larger samples of satellite populations, across a broad range of environments, together with predictions from theory. My group has developed techniques to measure satellite abundance, and plans to apply these to several forthcoming surveys. The final component of the program is to study the density of dark matter in and around individual galaxies. Theory predicts that galaxies in the inner regions of clusters should form earlier and have higher dark matter densities. We have recently tested this prediction in the Virgo cluster, and have detected a significant gradient in density with radial position. This technique provides a new, direct estimate of the assembly epoch of individual galaxies. We propose to apply it to other nearby galaxy clusters, but also to high-redshift samples with density constraints from dynamics or lensing. Together, these components should provide a richer theoretical understanding of halos and subhalos, new tools to study galaxy formation, and tighter constraints on the properties of dark matter.