Developing galaxy-cluster potentials into a cosmological diagnostic

尽管宇宙学标准模型取得了成功，但它声称的暗物质和暗能量仍然提出了迄今为止尚未解决的基本问题。其中一个问题与暗能量可能的时间演化有关，到目前为止还没有找到任何线索：从粒子物理学的角度来看，对暗能量最简单但同时也最不令人满意的解释是爱因斯坦的宇宙常数。对于我们对暗能量的理解，知道暗能量的密度是否在宇宙时间尺度上变化是至关重要的。也许唯一一群宇宙物体的演化足够敏感地依赖于暗能量可能的时间依赖关系，那就是星系团的种群。如果能够根据星系团的距离和至少一个内在参数对星系团进行足够可靠的计数，那么暗能量的时间演化就能以比目前更高的精度被追踪到。传统上，星系团的质量被用作内部参数来建立观测和理论预期之间的关系。然而，由于质量既不是直接可见的，也不能在理论上足够精确地预测，这种关系必须通过经验校准的标度关系来建立。尽管取得了很大的成功，但这些关系仍然非常分散，以至于它们很可能掩盖了暗能量对星系团数量的时间依赖性的影响。我们建议使用星系团的引力势而不是质量来将观测与理论联系起来。作为一个局部的、可直接测量的量，与质量相比，势具有决定性的优势。我们以前的工作已经展示了如何使用所有可用的星系团的可观测数据来确定势能，以及如何仅基于引力势从理论上表征星系团人口的统计数据。在这里提出的项目中，我们计划加入和整合我们迄今开发的方法，并从实际模拟的数据开始测试所产生的方法是否真的会以预期的方式减少宇宙学推断中的散射。首先，对现有数据的应用将使我们能够为即将到来的大型调查做准备。

Successful as the cosmological standard model is, its claim for dark matter and dark energy nonetheless poses hitherto unsolved fundamental questions. One of these questions concerns the possible time evolution of the dark energy, for which so far no clue could be found: The simplest, but at the same time least satisfactory explanation of dark energy from the point of view of particle physics is Einstein's cosmological constant. For our understanding of dark energy, it is fundamentally important to know whether the density of the dark energy is changing on cosmological time scales or not.Perhaps the only population of cosmic objects whose evolution depends sensitively enough on a possible time dependence of dark energy is the population of galaxy clusters. If it were possible to count galaxy clusters reliably enough depending on their distance and on at least one intrinsic parameter, a time evolution of the dark energy could be tracked down with substantially higher accuracy than so far possible.Conventionally, the mass of galaxy clusters is used as an internal parameter to establish the relation between observations and theoretical expectations. However, since the mass is neither directly observable nor can theoretically be predicted sufficiently precisely, this relation must be established by means of empirically calibrated scaling relations. Despite all successes, these relations still scatter so much that they are likely to veil the effects of a time dependence of the dark energy on the galaxy-cluster population.We propose to use the gravitational potential of the galaxy clusters instead of the mass to link observations with theory. As a local, directly measureable quantity, the potential has decisive advantages compared to the mass. Our previous work has shown how all available observables of galaxy clusters can be used to determine the potential and how the statistics of the galaxy-cluster population can be characterized theoretically based solely on the gravitational potential.In the project proposed here, we plan to join and integrate the methods we have so far developed, and to test beginning with realistically simulated data whether the resulting method will in fact reduce the scatter in the cosmological inference in the way expected. First applications to existing data will allow us to prepare for upcoming large surveys.