Developing galaxy-cluster potentials into a cosmological diagnostic

尽管宇宙学标准模型是成功的，但它对暗物质和暗能量的主张仍然提出了迄今为止尚未解决的基本问题。其中一个问题是关于暗能量可能的时间演化，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，最简单但同时最不令人满意的暗能量解释是爱因斯坦的宇宙常数。对于我们对暗能量的理解来说，知道暗能量的密度是否在宇宙学时间尺度上发生变化是至关重要的，也许唯一一个宇宙天体的演化足够敏感地依赖于暗能量可能的时间依赖性的群体是星系团的群体。如果能够根据星系团的距离和至少一个内禀参数足够可靠地计算星系团的数量，那么暗能量的时间演化就可以比目前更精确地追踪到。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，由于质量既不能直接观察到，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比例关系来建立。尽管取得了所有的成功，这些关系仍然分散，他们很可能掩盖暗能量的时间依赖性对星系团population.We建议使用星系团的引力势，而不是质量，将观测与理论联系起来。作为一个局部的、可直接测量的量，势与质量相比具有决定性的优势。我们之前的工作已经展示了如何利用星系团的所有可观测数据来确定引力势，以及如何仅基于引力势从理论上描述星系团人口的统计特征。在这里提出的项目中，我们计划加入和整合我们迄今为止开发的方法，并从实际模拟的数据开始，检验由此产生的方法是否真的会以预期的方式减少宇宙学推论中的分散。现有数据的首次应用将使我们能够为即将到来的大型调查做好准备。

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.