Cosmic ray physics in calculations of cosmological structure formation
Cosmic ray physics in calculations of cosmological structure formation
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宇宙射线物理学在宇宙结构形成计算中的应用
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
Cita
中科院分区：
文献类型：
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作者：
T. Ensslin;C. Pfrommer;V. Springel;Martin Jubelgas Mpa;Cita
宇宙射线（CR）在我们自己的银河系中起着决定性的作用。它们提供了对抗重力的分压支持，它们追踪了过去的高能事件，如超新星，它们通过它们的相互作用揭示了重子物质分布的基本结构。为了研究CRs对星系和宇宙结构形成与演化的影响，我们发展了一个近似的框架来处理宇宙学模拟中CRs的动力学和辐射效应。我们的指导原则是尝试在捕获尽可能多的CR种群的物理特性，同时需要尽可能少的额外计算资源之间找到平衡。我们近似的CR频谱的每个流体元素由一个单一的幂律，空间和时间变化的归一化，低能量截止，和频谱指数。粒子数，能量和压力的守恒原理，然后用于推导出描述CR谱的基本变量的演化方程，这是由于绝热和非绝热过程。考虑的过程包括压缩和稀疏，CR注射通过冲击超新星遗迹，注射在结构形成冲击波，在原位再加速CR，CR空间扩散，CR能量损失由于库仑相互作用，电离损失，韧致辐射损失，最后，强子与背景气体的相互作用，包括相关的γ射线和无线电发射由于随后的π衰变。我们表明，形式主义再现CR能量密度，压力，和冷却速率的准确度为10%，在稳态条件下，CR注射平衡冷却。因此，这是一个有前途的配方，允许模拟CR物理包括在内。最后，我们简要地讨论了如何形式主义可以包括在拉格朗日模拟方法，如光滑粒子流体动力学技术。因此，我们的框架非常适合被纳入星系和结构形成的数值模拟方案。
Cosmic rays (CRs) play a decisive role within our own Galaxy. They provide partial pressure support against gravity, they trace past energetic events such as supernovae, and they reveal the underlying structure of the baryonic matter distribution through their interactions. To study the impact of CRs on galaxy and cosmic structure formation and evolution, we develop an approximative framework for treating dynamical and radiative effects of CRs in cosmological simulations. Our guiding principle is to try to find a balance between capturing as many physical properties of CR populations as possible while at the same time requiring as little extra computational resources as possible. We approximate the CR spectrum of each fluid element by a single power-law, with spatially and temporally varying normalisation, low-energy cut-off, and spectral index. Principles of conservation of particle number, energy, and pressure are then used to derive evolution equations for the basic variables describing the CR spectrum, both due to adiabatic and non-adiabatic processes. The processes considered include compression and rarefaction, CR injection via shocks in supernova remnants, injection in structure formation shock waves, in-situ re-acceleration of CRs, CR spatial diffusion, CR energy losses due to Coulomb interactions, ionisation losses, Bremsstrahlung losses, and, finally, hadronic interactions with the background gas, including the associated γ-ray and radio emission due to subsequent pion decay. We show that the formalism reproduces CR energy densities, pressure, and cooling rates with an accuracy of ∼10% in steady state conditions where CR injection balances cooling. It is therefore a promising formulation to allow simulations where CR physics is included. Finally, we briefly discuss how the formalism can be included in Lagrangian simulation methods such as the smoothed particle hydrodynamics technique. Our framework is therefore well suited to be included into numerical simulation schemes of galaxy and structure formation.