星系形成的流体动力学模拟和半解析模型：同一枚硬币的两面
Hydrodynamical simulations and semi-analytic models of galaxy formation: two sides of the same coin
摘要：
在这项工作中，我们开发了一种新的方法，把一个国家的最先进的流体动力学宇宙学模拟的星系形成（HYD）到一个简单的半解析模型（SAM）。这是通过总结吸积，冷却，恒星形成的效率，和HYD给出的反馈，作为晕质量和红移的函数。令人惊讶的是，通过把HYD变成SAM，我们保存了单个星系的质量，在0.1德克斯的水平上，在一个对象一个对象的基础上。对于所有的红移，以及恒星和气体成分的质量都是如此，尽管对于低红移的卫星星系，协议达到0.2 dex。我们表明，即使SAM在每个星系中只使用一种气体，也可以获得相同的精度。此外，我们证明了一个大质量星系的形成历史提供了足够的信息，SAM再现整个宇宙学盒内的星系人口。HYD和SAM星系之间的小散射的原因是：a）效率匹配作为晕质量和红移的函数，这意味着合并树内的演化平均一致。b）对于一个给定的星系，效率在0.2-2 Gyr的时间尺度上围绕平均值波动。c）星系的各种质量分量是通过对效率随时间的变化进行积分，平均这些波动而获得的。我们将这里发现的效率与标准SAM配方进行比较，发现它们经常显著偏离。例如，这里的HYD显示了平滑的吸积作用，这对低质量的晕不太有效，并且总是由热的或稀释的气体组成;在高红移时冷却作用不太有效;恒星的形成只会随着宇宙时间的变化而轻微变化。这里开发的方法可以适用于一般的任何HYD，因此可以作为一个共同的语言HYDs和SAM（删节）。
英文摘要：
In this work we develop a new method to turn a state-of-the-art hydrodynamical cosmological simulation of galaxy formation (HYD) into a simple semi-analytic model (SAM). This is achieved by summarizing the efficiencies of accretion, cooling, star formation, and feedback given by the HYD, as functions of the halo mass and redshift. Surprisingly, by turning the HYD into a SAM, we conserve the mass of individual galaxies, with deviations at the level of 0.1 dex, on an object-by-object basis. This is true for all redshifts, and for the mass of stars and gas components, although the agreement reaches 0.2 dex for satellite galaxies at low redshift. We show that the same level of accuracy is obtained even in case the SAM uses only one phase of gas within each galaxy. Moreover, we demonstrate that the formation history of one massive galaxy provides sufficient information for the SAM to reproduce the population of galaxies within the entire cosmological box. The reasons for the small scatter between the HYD and SAM galaxies are: a) The efficiencies are matched as functions of the halo mass and redshift, meaning that the evolution within merger-trees agrees on average. b) For a given galaxy, efficiencies fluctuate around the mean value on time scales of 0.2-2 Gyr. c) The various mass components of galaxies are obtained by integrating the efficiencies over time, averaging out these fluctuations. We compare the efficiencies found here to standard SAM recipes and find that they often deviate significantly. For example, here the HYD shows smooth accretion that is less effective for low mass haloes, and is always composed of hot or dilute gas; cooling is less effective at high redshift; and star formation changes only mildly with cosmic time. The method developed here can be applied in general to any HYD, and can thus serve as a common language for both HYDs and SAM (Abridged).
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