星系中心的尖点：与观测的真实冲突还是宇宙学模拟的数值假象？
Cusps in the center of galaxies: a real conflict with observations or a numerical artefact of cosmological simulations?
摘要：
星系观测和N体宇宙学模拟产生了相互矛盾的星系中心区域的暗物质晕密度分布。虽然模拟表明该地区的尖点和普遍的密度分布（UDP），但大多数观测结果都倾向于中心有核心的可变分布。在本文中，我们调查的收敛性标准N体模拟，特别是在尖点区域，以下的方法提出的\protect{\citep{13}}。我们使用SPH程序Gadget-3模拟了著名的Hernquist模型，并考虑了粒子的全部动力学参数。我们发现，虽然尖形轮廓是稳定的，所有积分的运动特征个别粒子遭受强烈的非物理变化沿整个晕，揭示了有效的测试机构之间的相互作用。这一结果使人对模拟得到的速度分布函数的可靠性产生怀疑。此外，我们发现非物理的Fokker-Planck粒子流在尖点区域。同样的流应该出现在宇宙学的N体模拟，是强大到足以改变尖点的形状，甚至创建it. We的分析，基于Hernquist模型和标准的SPH代码，强烈表明，通常发现的宇宙学的N体模拟的UDP可能是一个后果的数值效应。一个更好地了解N体模拟收敛之前，一个“核心尖点问题”可以适当地用来质疑CDM模型的有效性是必要的。
英文摘要：
Galaxy observations and N-body cosmological simulations produce conflicting dark matter halo density profiles for galaxy central regions. While simulations suggest a cuspy and universal density profile (UDP) of this region, the majority of observations favor variable profiles with a core in the center. In this paper, we investigate the convergency of standard N-body simulations, especially in the cusp region, following the approach proposed by \protect{\citep{13}}. We simulate the well known Hernquist model using the SPH code Gadget-3 and consider the full array of dynamical parameters of the particles. We find that, although the cuspy profile is stable, all integrals of motion characterizing individual particles suffer strong unphysical variations along the whole halo, revealing an effective interaction between the test bodies. This result casts doubts on the reliability of the velocity distribution function obtained in the simulations. Moreover, we find unphysical Fokker-Planck streams of particles in the cusp region. The same streams should appear in cosmological N-body simulations, being strong enough to change the shape of the cusp or even to create it. Our analysis, based on the Hernquist model and the standard SPH code, strongly suggests that the UDPs generally found by the cosmological N-body simulations may be a consequence of numerical effects. A much better understanding of the N-body simulation convergency is necessary before a 'core-cusp problem' can properly be used to question the validity of the CDM model.
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