Anatomy of a Merger: Understanding the Dynamics of Galaxy Cluster Mergers

该团队将利用地面和太空望远镜的观测数据，研究暗物质粒子如何相互作用。宇宙的大部分质量是以非辐射的形式存在的，也就是“暗”物质。暗物质粒子对引力有反应，但对它们知之甚少。一个重要的基本步骤是测量暗物质粒子之间相互作用的强度，而不受重力的影响。当物理学家想要研究亚原子粒子的基本性质时，他们会在昂贵的人造对撞机中将它们撞在一起。幸运的是，大自然以星系团合并的形式免费提供了暗物质对撞机。该团队将分析几十个星团碰撞的“刹车痕迹”，并利用这些结果来研究暗物质粒子如何在不受重力影响的情况下相互作用。对于更广泛的影响，PI指出，四年制大学的学生在申请博士课程的实用性方面可能会遇到信息差距。为了缩小这一差距，PI将继续运行他的广受欢迎的研究生物理入学训练营，为北加州的机构提供服务。该提议的目的是结合多波长观测和模拟合并星系团的集合，以约束暗物质粒子的“自相互作用横截面”。合并的星团可以被认为是暗物质对撞机。引力透镜被用作绘制暗物质粒子分布图的工具。集群成员数据用于确定碰撞的年龄。有了这些信息，模拟可以用来约束暗物质粒子相互作用的强度（“自相互作用截面”），以重现碰撞的快照。如果研究合并星团的整体，而不是只研究一个，这种技术会变得更强。该建议将该技术应用于合并集群的集合。此外，该提案还采取了新颖的步骤，要求合并显示无线电遗迹。这个要求很重要，因为它提供了关于合并年龄的额外的、独立的信息，也确保了天空的观测角度将最大化所寻求的效果。

The team will use observational data, from telescopes on the ground and in space, to study how particles of dark matter interact with each other. Much of the mass of the Universe is in the form of non-radiating, thus "dark", matter. Particles of dark matter respond to the force of gravity, but little else is known about them. An important, basic step is to measure how strongly dark-matter particles interact with each other, independent of gravity. When physicists want to investigate the basic properties of sub-atomic particles, they smash them together in expensive man-made colliders. Fortunately, Nature has provided dark-matter colliders, for free, in the form of merging clusters of galaxies. The team will analyze the "skid marks" of a few dozen cluster collisions and use the results to study how the dark-matter particles interact with each other, independent of gravity.For broader impacts, the PI has noted that students in four-year colleges can experience an information gap regarding the practicalities of applying to PhD programs. In an attempt to close this gap, the PI will continue running his popular Graduate Physics Admission Boot Camp that serves institutions in northern California.The aim of the proposal is to combine multi-wavelength observations and simulations of an ensemble of merging galaxy clusters to constrain the "self-interaction cross-section" of dark-matter particles. The merging clusters can be thought of as dark-matter colliders. Gravitational lensing is used as a tool to map out the distribution of the dark-matter particles. Cluster membership data are used to age-date the collision. Given this information, simulations can be used to constrain how strongly the dark-matter particles need to interact with each other (the "self-interaction cross-section") to reproduce the snapshot of the collision. This technique becomes stronger if an ensemble of merging clusters is studied, instead of only one. The proposal will apply the technique to an ensemble of merging clusters. Moreover, the proposal also takes the novel step of requiring that the mergers exhibit radio relics. This requirement is important because it provides extra, independent information about the merger ages and also ensures the plane-of-sky viewing angles that will maximize the effects being sought.