Understanding and Tracing Dark Matter in the Local Universe

理解和追踪本地宇宙中的暗物质

• 批准号: RGPIN-2019-04666
• 负责人: Taylor, James
• 金额: $ 1.75万
• 依托单位: University of Waterloo
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=715100
• 关键词: Understanding; Tracing; Dark; Matter; Local

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.

暗物质将我们在宇宙中看到的大尺度可见结构结合在一起，提供了密集的“光环”，在其中形成了单个星系、星系群和星系团。然而，暗物质的基本性质仍然未知，建立它与粒子物理标准模型的其余部分的关系仍然是宇宙学的首要任务。在大尺度上，暗物质的聚集性是众所周知的，观测和理论预测也是一致的。在小尺度上，我们的观测探测器要少得多，暗物质的行为也更具争议。新的和即将进行的调查有望极大地改善这种情况，对星系团和引力透镜的测量要灵敏得多。理论家面临的挑战是跟上形势，做出足够准确的预测，以便充分利用这些数据。这是我提出的研究计划的目标，该计划包括三个主要部分。 第一个组成部分是了解暗物质晕在反复合并过程中是如何演变的。我已经开始了一个主要的光晕合并的模拟程序，以了解光晕的结构属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。我们还打算研究微小的合并，这决定了单个星系如何以群体和星系团的形式演化。 第二个部分是通过定义微弱卫星星系的局部样本并将它们与模拟进行比较，来追踪暗物质的亚结构，并表征小尺度上星系形成的效率。银河系的矮小卫星比最简单的理论模型预测的要少，这就是著名的“卫星失踪问题”。然而，在星系团中，情况却截然不同，矮星似乎很多。为了解决星系形成在哪里以及为什么逐渐减少，我们需要更多的卫星样本，覆盖广泛的环境，再加上理论上的预测。我的团队已经开发出测量卫星丰度的技术，并计划将这些技术应用于即将到来的几项调查。 该计划的最后一个组成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，暗物质密度更高。我们最近在室女座星系团中测试了这一预测，并检测到了密度与径向位置的显著梯度。这项技术提供了一种新的、直接的对单个星系的组装时代的估计。我们建议将它应用于附近的其他星系团，但也适用于受动力学或透镜效应限制的高红移样本。 总而言之，这些成分应该会提供对光晕和次光晕的更丰富的理论理解，为研究星系形成提供新的工具，并对暗物质的性质提供更严格的约束。