WEFT 项目：I. 宇宙纤维状结构中的湍流涌现
The WEFT project: I. The emergence of turbulence in a cosmic filament
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中文总结 AI 辅助
WEFT 项目首次模拟揭示宇宙纤维状结构中湍流通过层级合并与斜压涡量产生而涌现，并发展为间歇性级联，为观测 WHIM 提供湍流输入。
中文摘要 AI 辅助
当今宇宙中的大部分普通物质仍然逃避直接探测。这些缺失的重子被认为存在于贯穿宇宙网的纤维状结构中的温热星系际介质（WHIM）中，其湍流和热状态仍缺乏约束，而这却是任何观测尝试的基础。除了观测上的重要性，这种湍流如何涌现——引力坍缩将有序流入转化为无序级联——本身也是一个结构形成问题。我们在“纤维状结构中的网络演化目标放大模拟”（WEFT）项目的首次模拟中，刻画了宇宙纤维状结构中弥散气体从形成到今天的湍流涌现过程。宇宙学放大技术被应用于单一纤维状结构，使用移动网格代码 AREPO 从 z=63 演化到 z=0，中位气体单元尺寸约为 8 kpc。我们追踪了纤维状结构的组装、其弥散气体的热力学状态、在吸积激波处涡量的产生以及湍流运动的增长，然后通过高阶速度结构函数及其从扩展自相似性得到的相对标度指数来量化级联的间歇性。该纤维状结构通过多个原纤维状结构的层级合并而非层流吸积而组装。涡量在旋转流束斜向遇到其吸积激波处由斜压机制产生。流动从超音速、激波主导的状态（统计上接近双分形 Burgers 极限）演化为充分发展的、轻微超音速的间歇性级联，其纵向指数在 z=0 时最接近片状 She-Lévêque 模型。因此，湍流是纤维状结构弥散气体的内在、可量化的属性。这次探路者运行提供了 WHIM 可观测性预测的湍流输入。
英文摘要
Much of the ordinary matter in the present-day Universe still escapes direct detection. These missing baryons are thought to reside in a warm-hot intergalactic medium (WHIM) threading the filaments of the cosmic web, whose turbulent and thermal state remains poorly constrained yet underpins any attempt to observe it. Beyond its observational stakes, how this turbulence emerges, as gravitational collapse converts ordered inflow into a disordered cascade, is a question of structure formation in its own right. We characterise the emergence of turbulence in the diffuse gas of a cosmic filament, from its assembly to the present day, in the first simulation of the Web Evolution in Filament Targeted zoom simulations (WEFT) project. The cosmological zoom-in technique is applied to a single filament, evolved from z=63 to z=0 with the moving-mesh code AREPO, reaching a median gas cell size of ~8 kpc. We trace the filament assembly, the thermodynamic state of its diffuse gas, the generation of vorticity at its accretion shocks, and the growth of turbulent motions, then quantify the intermittency of the cascade through high-order velocity structure functions and their relative scaling exponents from extended self-similarity. The filament assembles by the hierarchical merging of several proto-filaments rather than by laminar accretion. Vorticity is seeded baroclinically where the rotating strands meet their accretion shocks obliquely. The flow evolves from a supersonic, shock-dominated state, statistically close to the bifractal Burgers limit, into a developed, mildly supersonic, intermittent cascade whose longitudinal exponents lie closest to the sheet-like She-Lévêque model at z=0. Turbulence is thus an intrinsic, quantifiable property of the diffuse gas of filaments. This pathfinder run provides the turbulent input for forecasts of WHIM observability.
发表机构
- Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）
- Astrophysics Research Center of the Open University (ARCO), The Open University of Israel（以色列开放大学天体物理研究中心）
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