再见 Kolmogorov：超新星驱动的多相星际介质中的正向与反向湍流级联
So long Kolmogorov: the forward and backward turbulence cascades in a supernovae-driven, multiphase interstellar medium
AI总结：
本研究利用高分辨率模拟探究超新星驱动多相星际介质的湍流级联，发现不可压缩模式存在高度非局部级联与反向级联，揭示了其与传统 Kolmogorov 模型的显著偏差。
摘要：
盘状星系的星际介质（ISM）是湍流的，然而 ISM 湍流的基本性质——能量级联——尚未得到详细理解。在本研究中，我们使用流体力学、重力分层、超新星（SNe）驱动的多相 ISM 的高分辨率模拟，来探究星系湍流级联的性质。通过使用分为可压缩 $\mathbf{u}_c$ 和不可压缩 $\mathbf{u}_s$ 模式之间相互作用的速度通量传递函数，我们表明，当由额外的 $\mathbf{u}_s$ 模式介导时，$\mathbf{u}_c$ 和 $\mathbf{u}_s$ 中都存在从大尺度到小尺度的级联。但 $\mathbf{u}_s$ 级联是高度非局部的。此外，$\mathbf{u}_s$ 级联中存在一个由 $\mathbf{u}_c$ 介导的分量，其进行方向相反——即从小尺度到大尺度的反向级联。该级联将通量注入远超标高的尺度，为风提供能量并为正向级联提供燃料。强非局部和反向 $\mathbf{u}_s$ 级联都发生在具有幂律 $\mathbf{u}_s$ 能谱的尺度上，突显了该能谱对真实底层物理过程的简并性。我们直接表明，反向级联来自于 $\mathbf{u}_s$ 模式与膨胀 SNe 遗迹（SNRs）的相互作用，并且 $\mathbf{u}_s$ 模式主要通过这些 SNRs 中暖气体（$T\lesssim 10^4\\,\rm{K}$）与热气体（$T\gg10^4\\,\rm{K}$）之间的斜压、高度褶皱冷却层产生至主导阶。最后，我们概述了星系盘中 SNe 驱动湍流的完整现象学，估计了由 SNR 冷却层产生的 $10^{-16}\\,\rm{G}$ Biermann 场，并强调了 SNe 驱动湍流与传统 Kolmogorov 模型的强烈偏差。
英文摘要：
The interstellar medium (ISM) of disk galaxies is turbulent, and yet the fundamental nature of ISM turbulence, the energy cascade, is not understood in detail. In this study, we use high-resolution simulations of a hydrodynamical, gravitationally stratified, supernova (SNe)-driven, multiphase ISM to probe the nature of a galactic turbulence cascade. Through the use of velocity flux transfer functions split into interactions between compressible $\mathbf{u}_c$ and incompressible $\mathbf{u}_s$ modes, we show that there exists a large-to-small-scale cascade in both $\mathbf{u}_c$ and $\mathbf{u}_s$ when mediated by an additional $\mathbf{u}_s$ mode. But the $\mathbf{u}_s$ cascade is highly non-local. Moreover, there is a $\mathbf{u}_c$ mediated component of the $\mathbf{u}_s$ cascade that proceeds in the opposite direction -- an inverse cascade from small-to-large scales. The cascade feeds flux into scales well beyond the scale height, energizing the winds and fueling the direct cascades. Both the strongly non-local and the inverse $\mathbf{u}_s$ cascades happen on scales that have a power law $\mathbf{u}_s$ energy spectrum, highlighting how degenerate the spectrum is to the true underlying physical processes. We directly show that the inverse cascade comes from $\mathbf{u}_s$ modes interacting with expanding SNe remnants (SNRs) and that $\mathbf{u}_s$ modes are generated to leading order via baroclinic, highly corrugated cooling layers between warm $(T\lesssim 10^4\,\rm{K})$ and hot $(T\gg10^4\,\rm{K})$ gas in these SNRs. Finally, we outline a complete phenomenology for SNe-driven turbulence in a galactic disk, estimate a $10^{-16}\,\rm{G}$ Biermann field generated from SNR cooling layers, and highlight the strong deviations that SNe-driven turbulence has from the conventional Kolmogorov model.
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