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arXiv 0810.0277astro-ph
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LCDM晕暗物质相空间密度分布的演化

Evolution of the Dark Matter Phase-Space Density Distributions of LCDM Halos

Ileana Vass, Monica Valluri, Andrey Kravtsov, Stelios Kazantzidis

备注：
Closely matches version accepted for publication
发表信息：
Mon.Not.Roy.Astron.Soc.395:1225-1236,2009
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摘要：

我们研究了LCDM晕的分级结构形成过程中相空间密度的演化。我们计算了相空间密度（Q）的球平均替代物和暗物质粒子的粗粒度分布函数f（x，v），这些粒子位于四个Milky Way大小的暗物质晕的~2维里半径内。估计的f（x，v）在任何半径上跨越四十年。在$z=0$的银河系大小的DM晕的两个维里半径范围内结束的暗物质粒子在早期红移时具有近似高斯分布的log（f），但在较低的红移时，分布变得越来越偏斜。对应于高斯峰的值随着演化的进行而减小，并且由（1+z）中的幂律很好地描述。最高的f值出现在暗物质晕和暗物质晕的中心，这里的f值可能比主晕中心高一个数量级。幂律Q（r）曲线可能反映了熵的分布（K = σ ^2/rho^{2/3} \propto r^{1.2}），这是暗物质在吸积到不断增长的晕上时获得的。另一方面，估计的f（x，v）表现出更复杂的行为。虽然中间粗粒相空间密度分布F（r）在晕圈内部区域可用幂律近似，但在较大半径处，分布明显变小。这是因为在小尺度上平均的相空间密度对与幸存的subhalos相关的高f材料以及由破裂的subhalos产生的相对未混合的材料（可能在流中）敏感，这在大半径处贡献了相当大的一部分物质。（简略）

英文摘要：

We study the evolution of phase-space density during the hierarchical structure formation of LCDM halos. We compute both a spherically-averaged surrogate for phase-space density (Q) and the coarse-grained distribution function f(x,v) for dark matter particles that lie within~2 virial radii of four Milky-Way-sized dark matter halos. The estimated f(x,v) spans over four decades at any radius. Dark matter particles that end up within two virial radii of a Milky-Way-sized DM halo at $z=0$ have an approximately Gaussian distribution in log(f) at early redshifts, but the distribution becomes increasingly skewed at lower redshifts. The value corresponding to the peak of the Gaussian decreases as the evolution progresses and is well described by a power-law in (1+z). The highest values of f are found at the centers of dark matter halos and subhalos, where f can be an order of magnitude higher than in the center of the main halo. The power-law Q(r) profile likely reflects the distribution of entropy (K = sigma^2/rho^{2/3} \propto r^{1.2}), which dark matter acquires as it is accreted onto a growing halo. The estimated f(x, v), on the other hand, exhibits a more complicated behavior. Although the median coarse-grained phase-space density profile F(r) can be approximated by a power-law in the inner regions of halos and at larger radii the profile flattens significantly. This is because phase-space density averaged on small scales is sensitive to the high-f material associated with surviving subhalos, as well as relatively unmixed material (probably in streams) resulting from disrupted subhalos, which contribute a sizable fraction of matter at large radii. (ABRIDGED)

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