Implementing Feedback in Simulations of Galaxy Formation: A Survey of Methods
Implementing Feedback in Simulations of Galaxy Formation: A Survey of Methods
复制标题
在星系形成模拟中实施反馈：方法综述
DOI：
10.1086/317828
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
H. Couchman
中科院分区：
文献类型：
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作者：
R. Thacker;R. Thacker;R. Thacker;H. Couchman;H. Couchman
我们提出了一个详细的描述，并检查性能，一些不同的方法来模拟星系形成的反馈。气体动力使用平滑粒子流体动力学（SPH）进行评估。星星形成和超新星反馈包括使用一个三参数模型，确定星星形成率（SFR）的归一化，反馈能量，和反馈区域的寿命。星星的形成率计算的所有气体粒子落在规定的温度，密度和收敛流的标准，宇宙学模拟，我们还包括气体粒子的自引力标准，以防止星星形成在高红移。拉格朗日施密特定律被用来从SPH密度计算星星形成率。当气体粒子的星星质量超过一定限度时，通常是气体粒子质量的一半，气体转化为恒星。通过将预先计算的能量作为热加热返回到ISM来并入反馈。我们比较了将这种能量分布在平滑尺度上或将其沉积在单个粒子上的效果。通过调整辐射冷却中使用的密度，使能量在设定的半衰期内衰减，或者通过完全关闭冷却并允许反馈区域短暂的绝热膨胀，可以防止加热粒子的辐射损失。我们测试模型的星系形成宇宙学的初始条件，也孤立的盘星系。对于银河系和矮星系NGC 6503的孤立原型，我们发现反馈具有显着的效果，一些算法能够从暗物质晕中释放气体（“吹走”）。正如预期的那样，反馈对矮星系有更强的影响，产生显着的盘蒸发，也有更大的反馈“气泡”相同的参数。在临界密度CDM宇宙学模拟，发展到红移z = 1，我们发现，除非极端的模型，反馈几乎没有影响。此外，反馈只能产生一个特定的角动量值的磁盘，大约是没有反馈的运行的两倍，因此磁盘具有特定的角动量值，这是观察到的椭圆星系的特征。我们认为，这是一个极端的中央浓度的暗晕在标准的CDM模型和普遍的核心晕角动量传输机制（即使在光反馈）的结果。相对于我们的基准模型，一个具有极其剧烈反馈的模拟导致了一个类似于z = 1的其他模拟的圆盘，并且具有一个特定的角动量值，这在观察到的圆盘星系中更为典型。在z = 0.5的时候，大量的没有角动量亏损的晕气体出现;然而，冷却时间太长，无法吸积到盘上。我们进一步指出，在分层模拟中形成的磁盘部分是由模拟的最小质量尺度作为一个高效的“支持”机制所产生的数值工件。SPH方法中致密区域的处理对盘的形成有很大影响。在SPH中处理高密度区域所固有的问题，与代表分层形成过程的困难相一致，意味着星系形成的真实模拟需要比目前使用的更高的粒子分辨率。
We present a detailed description, and examine the performance of, a number of different approaches to modeling feedback in simulations of galaxy formation. Gasdynamic forces are evaluated using smoothed particle hydrodynamics (SPH). Star formation and supernova feedback are included using a three-parameter model which determines the star formation rate (SFR) normalization, feedback energy, and lifetime of feedback regions. The star formation rate is calculated for all gas particles which fall within prescribed temperature, density, and convergent flow criteria, and for cosmological simulations we also include a self-gravity criterion for gas particles to prevent star formation at high redshifts. A Lagrangian Schmidt law is used to calculate the star formation rate from the SPH density. Conversion of gas to stars is performed when the star mass for a gas particle exceeds a certain limit, typically half that of the gas particle. Feedback is incorporated by returning a precalculated amount of energy to the ISM as thermal heating. We compare the effects of distributing this energy over the smoothing scale or depositing it on a single particle. Radiative losses are prevented from heated particles by adjusting the density used in radiative cooling so that the decay of energy occurs over a set half-life, or by turning off cooling completely and allowing feedback regions a brief period of adiabatic expansion. We test the models on the formation of galaxies from cosmological initial conditions and also on isolated disk galaxies. For isolated prototypes of the Milky Way and the dwarf galaxy NGC 6503 we find feedback has a significant effect, with some algorithms being capable of unbinding gas from the dark matter halo ("blow-away"). As expected feedback has a stronger effect on the dwarf galaxy, producing significant disk evaporation and also larger feedback "bubbles" for the same parameters. In the critical-density CDM cosmological simulations, evolved to a redshift z = 1, we find that, barring extreme models, feedback has little effect. Further, feedback only manages to produce a disk with a specific angular momentum value approximately twice that of the run with no feedback, the disk thus has an specific angular momentum value that is characteristic of observed elliptical galaxies. We argue that this is a result of the extreme central concentration of the dark halos in the standard CDM model and the pervasiveness of the core-halo angular momentum transport mechanism (even in light of feedback). A simulation with extremely violent feedback, relative to our fiducial models, leads to a disk that resembles the other simulations at z = 1 and has a specific angular momentum value that is more typical of observed disk galaxies. At later times, z = 0.5, a large amount of halo gas which does not suffer an angular momentum deficit is present; however, the cooling time is too long to accrete on to the disk. We further point out that the disks formed in hierarchical simulations are partially a numerical artifact produced by the minimum mass scale of the simulation acting as a highly efficient "support" mechanism. Disk formation is strongly affected by the treatment of dense regions in the SPH method. The problems inherent in the treatment of high-density regions in SPH, in concert with the difficulty of representing the hierarchical formation process, means that realistic simulations of galaxy formation require far higher particle resolution than currently used.