Structure Formation with Ultralight Axion Dark Matter
Structure Formation with Ultralight Axion Dark Matter
复制标题
使用超轻 Axion 暗物质形成结构
DOI：
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
X. Du
中科院分区：
文献类型：
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作者：
X. Du
超轻轴子是一个质量极小的标量场。它被提出作为标准冷暗物质（CDM）的替代暗物质候选者。如果轴子之间的自相互作用可以忽略，它也被称为模糊暗物质（FDM）。在大尺度上，FDM的行为类似于CDM，产生与当前观测一致的大尺度宇宙结构。但在金斯长度以下的尺度上，标量场相干振荡产生的量子压力抵消了重力，导致结构形成和核心暗物质晕轮廓的大幅抑制。本文主要讨论了FDM场景下宇宙结构的形成。首先，我将展示如何将FDM实现到用于星系形成的公开的半解析代码GALACTICUS中。利用改进后的代码，计算了具有不同粒子质量和密度分数的FDM的（子）晕质量函数。与标准CDM相比，发现（亚）晕质量函数在较低质量下被很大程度地抑制。抑制尺度与FDM质量的平方根成反比。然后，基于FDM光晕每次双星合并时的核心质量增长，提出了模拟观测到的核心-光晕质量关系的简单模型。利用修改后的GALACTICUS代码对模型进行了验证。最后，为了研究FDM亚光晕核心的潮汐破坏，我使用四阶伪谱方法进行了理想模拟。数值计算得到的岩心潮汐剥落质量损失率与以往半解析处理的结果进行了比较。我们发现，经过一些重新解释，两个结果是相当一致的。将数值结果应用到GALACTICUS中，计算了考虑和不考虑核心剥离的亚晕质量函数。最后给出了亚光晕质量函数的拟合公式，这将为今后从与光晕子结构有关的观测中约束FDM的研究提供参考。
Ultralight axion is a scalar field with an extremely small mass $sim10^{-22} eV$. It is proposed as an alternative dark matter candidate to the standard cold dark matter (CDM). If self-interactions between axions can be ignored, it is also called fuzzy dark matter (FDM). On large scales, FDM behaves like CDM producing large scale structure of the Universe consistent with current observations. But on scales below the Jeans length, quantum pressure arising from coherent oscillations of the scalar filed counters gravity, leading to a large suppression in the structure formation and cored dark matter halo profiles. In this dissertation, I mainly discuss the cosmic structure formation in the scenario of FDM. First, I show how we implement FDM into the publicly available semi-analytic code for galaxy formation, GALACTICUS. With the modified code, we compute the (sub)halo mass function for FDM with different particle masses and density fractions. Comparing to the standard CDM, the (sub)halo mass function is found to be largely suppressed at lower masses. The suppression scale is inversely proportional to the square root of FDM mass. Then, based on the core mass growth in each binary merger of FDM halos, a simple model for the core-halo mass relation observed in simulations is proposed. The model is verified using the modified GALACTICUS code. Finally, to study tidal disruption of FDM subhalo cores, I perform idealized simulations using a fourth-order pseudo-spectral method. The core mass loss rate due to tidal stripping obtained numerically is compared with the previous results from semi-analytic treatments. We find after some reinterpretations, two results are reasonably consistent. Implementing the numerical results into GALACTICUS, I compute the subhalo mass function with and without considering the core stripping. Fitting formula for the subhalo mass function is given at the end, which will be useful in future studies on constraining FDM from observations related to halo substructure.