Structure Formation with Ultralight Axion Dark Matter

超光轴子(ULA)是暗物质的候选者，它受到粒子物理学的很好的激励，并产生了以前从未探索过的新的天体物理现象。关于宇宙学结构的形成，它们的性质与大尺度上的正则冷暗物质范例没有什么区别。相比之下，在小尺度上，微扰的引力增长被抑制在具有维里速度的粒子的德布罗意波长所给出的所谓“量子牛仔长度”以下。ULA暗物质在小尺度上的波状性质和具有孤子性质的基态解的存在刺激了对丰富现象学的探索，包括光晕和光晕下质量函数的低质量截断，与观测到的矮小星系旋转曲线一致的孤子光晕核心，以及暗物质和恒星成分的显著减少的弛豫时间。至关重要的是，目前还不可能基于达到N体模拟标准的宇宙学模拟做出定量预测。人们迫切需要新的计算方法来填补这一空白。我们建议使用一种新的混合计算方案来模拟ULA暗物质的宇宙结构形成，该暗物质目前正在由我们的小组开发和测试。它使用现有Enzo程序的自适应网格精化，将基于粒子的半经典方法在粗网格水平上求解薛定谔-泊松方程与在最精细水平上基于网格的求解器相结合。我们打算首次使用新的混合方法结合Enzo的重子物理和恒星分量模块的放大模拟来研究具有ULA暗物质的星系的形成和演化。此外，我们还计划研究日晕的子结构演化，包括亚晕质量函数，以及ULA晕中的驰豫效应和动力摩擦。

Ultralight axions (ULAs) are dark matter candidates that are very well motivated from particle physics and give rise to new, previously unexplored astrophysical phenomena. With respect to cosmological structure formation, their properties are indistinguishable from the canonical cold dark matter paradigm on large scales. On small scales, in contrast, the gravitational growth of perturbations is suppressed below the so-called ``quantum Jeans length'' given by the de Broglie wavelength of particles with virial velocities. The wave-like nature of ULA dark matter on small scales and the existence of ground-state solutions with solitonic properties have stimulated the exploration of a rich phenomenology, including a low-mass cutoff of the halo and subhalo mass functions, solitonic halo cores consistent with observed dwarf galaxy rotation curves, as well as significantly reduced relaxation times for dark matter and stellar components. Crucially, it is impossible at the present time to make quantitative predictions based on cosmological simulations reaching the standards of N-body simulations. There is a strong demand for new computational methods to fill this gap. We propose to use a novel hybrid computational scheme to simulate cosmological structure formation with ULA dark matter that is currently being developed and tested by our group. Using adaptive mesh refinement of the existing Enzo code, it combines a particle-based semi-classical method for solving the Schrödinger-Poisson equation on coarse mesh levels with a grid-based solver on the finest level.We intend to study, for the first time, the formation and evolution of galaxies with ULA dark matter, using zoom-in simulations with the new hybrid method combined with Enzo's modules for baryonic physics and stellar components. Furthermore, we plan to investigate the substructure evolution of halos including the subhalo mass function as well as relaxation effects and dynamical friction in ULA halos.