湍流多相星际介质的半解析模型
A semi-analytic model of the turbulent multi-phase interstellar medium
摘要：
我们提出了一个半解析模型的星际介质，认为当地的过程和结构的湍流恒星形成气体。一个体积元素的星际介质被描述为一个多相系统，包括一个冷的和一个温暖的气体相在有效的（热加湍流）压力平衡，和恒星组件。由于湍流对气相的形状、分子氢的产生和恒星的形成有着至关重要的影响，因此对湍流能量--未解决运动的动能--的一致处理是我们模型的一个重要的新特征。除了超新星和冷却不稳定性产生的湍流外，我们还考虑了大尺度运动的强迫。我们制定了一套常微分方程，统计描述恒星的形成和不同的预算之间的质量和能量的交换在一个区域的星际介质与给定的平均密度，大小，金属丰度和外部湍流强迫。通过探索解的行为，我们发现了平衡态，在平衡态中恒星形成效率与观测结果一致。Kennicutt-Schmidt关系自然产生于平衡解，而传统的恒星形成模型在数值模拟中将这种关系与观测到的效率参数作为唯象校准。除了半解析的方法，一个潜在的应用是一个完整的亚网格尺度模型的未解决的多相结构，恒星的形成和湍流的模拟星系或宇宙学模拟。本文中提出的公式结合了专注于特定过程的各种模型，但可以用于特定应用，这取决于解析长度尺度的范围。
英文摘要：
We present a semi-analytic model for the interstellar medium that considers local processes and structures of turbulent star-forming gas. A volume element of the interstellar medium is described as a multiphase system, comprising a cold and a warm gas phase in effective (thermal plus turbulent) pressure equilibrium, and a stellar component. Since turbulence has a critical impact on the shape of the gaseous phases, on the production of molecular hydrogen and on the formation of stars, the consistent treatment of turbulence energy -- the kinetic energy of unresolved motions -- is an important new feature of our model. Besides turbulence production by supernovae and by the cooling instability, we also take into account the forcing by large scale motions. We formulate a set of ordinary differential equations, which statistically describes star formation and the exchange between the different budgets of mass and energy in a region of the interstellar medium with given mean density, size, metallicity and external turbulence forcing. By exploring the behaviour of the solutions, we find equilibrium states, in which the star formation efficiencies are consistent with observations. Kennicutt-Schmidt-like relations naturally arise from the equilibrium solutions, while conventional star formation models in numerical simulations impose such relations with observed efficiency parameters as phenomenological calibrations. Beyond the semi-analytic approach, a potential application is a complete subgrid scale model of the unresolved multi-phase structure, star formation and turbulence in simulations of galaxies or in cosmological simulations. The formulation presented in this article combines various models focusing on particular processes and yet can be adopted to specific applications, depending on the range of resolved length scales.
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