The Cosmic History of Baryons

AST 98-02568 David H. Weinberg Weinberg 博士建议与 Katz 博士（马萨诸塞大学）和 Hernquist 博士（加州大学圣克鲁斯分校）合作进行数值模拟，模拟从 z ~ 8 到 z=0 的宇宙重子成分的宇宙历史，特别关注 Ly a 森林、高红移星系以及当地星系和星系间气体的分布宇宙。 他们计划使用 TreeSPH——一种数值模拟代码，它将重力分量的分层树 N 体算法与气体分量的平滑粒子流体动力学 (SPH) 相结合。 该代码现在以并行形式存在。 根据主要的宇宙学理论，我们今天观察到的星系和大尺度结构是由于早期宇宙小幅度波动的引力不稳定性而增长的。 无碰撞暗物质的引力聚集推动了大尺度质量分布的演化，但天文观测几乎完全依赖于恒星或气体发射（或在某些情况下吸收）的电磁辐射。 流体动力学模拟结合了影响宇宙重子分布演化的非引力物理学，极大地增强了宇宙学理论的预测和解释能力。 模拟的初步结果表明，冷暗物质情景的几种变体预测了大量的高红移星系。 该团队正在研究不同场景下莱曼断裂星系的聚集。 流体动力学模拟表明，低柱密度 Ly 森林主要出现在弥漫的、平稳波动的星系间气体中。 这种介质的物理原理非常简单，允许模拟在给定特定的宇宙学模型的情况下做出稳健的定量预测。 由 QSO 吸收数据支持的高红移结构模拟表明，大多数高红移重子存在于产生 Ly 森林的扩散介质中，其中较小部分存在于星系和热气晕中。 ***

AST 98-02568 David H. Weinberg Dr. Weinberg proposes to work with Dr. Katz (University of Massachusetts) and Dr. Hernquist (University of California, Santa Cruz) to conduct numerical simulations that model the cosmic history of the baryon component of the universe from z ~ 8 to the z=0, with particular attention to the Ly a forest, high redshift galaxies and the distributions of galaxies and intergalactic gas in the local universe. They plan to use TreeSPH - a numerical simulation code that combines a hierarchical tree N-body algorithm for gravitational components with smoothed particle hydrodynamics (SPH) for the gas component. The code now exists in parallel form. According to the leading cosmological theories, the galaxies and large scale structure that we observe today grew by gravitational instability from small-amplitude fluctuations in the early universe. Gravitational clustering of collisionless dark matter drives the evolution of the mass distribution on large scales, but astronomical observations reply almost exclusively on electromagnetic radiation that has been emitted (or in some cases absorbed) by stars or gas. Hydrodynamic simulations, which incorporate the non-gravitational physics that influences the evolution of the cosmic baryon distribution, dramatically enhance the predictive and explanatory power of cosmological theories. Preliminary results from the simulations show that a substantial population of high redshift galaxies is predicted by several variants of the cold dark matter scenario. The team is studying the clustering of Lyman break galaxies in different scenarios. Hydrodynamic simulations show that the low column density Ly a forest arises primarily in diffuse, smoothly fluctuating, intergalactic gas. The physics of this medium is remarkably simple, allowing the simulations to make robust, quantitative predictions given a specified cosmological model. Simulations of high redshift structure, supported by QSO absorption data, indicate that most of t he high redshift baryons reside in the diffuse medium that produces the Ly a forest, with smaller fractions in galaxies and hot gas halos. ***