Dark matter distribution in dwarf spheroidal galaxies
Dark matter distribution in dwarf spheroidal galaxies
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DOI：
10.1046/j.1365-8711.2002.05457.x
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发表时间：
2002-07
影响因子：
4.8
通讯作者：
E. Łokas
中科院分区：
文献类型：
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作者：
E. Łokas
我们通过模拟矮球状星系视距速度分布的矩来研究暗物质在它们中的分布。我们讨论了不同的暗物质密度分布，包括cuspy和具有平坦密度核。在具有不同速度分布的双组分（恒星和暗物质）球面系统的标准动力学理论框架下进行了预测。我们将预测的速度色散曲线与天炉座和天龙座矮星的观测结果进行了比较。对于各向同性模型，发现具有核心的暗晕比具有尖端的暗晕更适合数据。通过对数据拟合暗质量和速度各向异性两个参数，研究了各向异性模型。在这种情况下，所有的剖面都可以很好地拟合，但是剖面的尖端越陡峭，拟合数据所需的速度分布就越切线。为了解决这种众所周知的密度剖面相对于速度各向异性的退化，我们获得了对最适合速度色散剖面的模型的视距速度分布峰度的预测。事实证明，有岩心的剖面通常会产生更高的峰度值，而峰度值随着距离的增加而下降得更快，这将使我们能够在峰度测量可用时区分不同的剖面。我们还表明，以目前的数据质量，还不能排除用修正牛顿动力学来解释速度色散的可能性。
We study the distribution of dark matter in dwarf spheroidal galaxies by modelling the moments of their line-of-sight velocity distributions. We discuss different dark matter density profiles, both cuspy and possessing flat density cores. The predictions are made in the framework of standard dynamical theory of two-component (stars and dark matter) spherical systems with different velocity distributions. We compare the predicted velocity dispersion profiles to observations in the case of Fornax and Draco dwarfs. For isotropic models the dark haloes with cores are found to fit the data better than those with cusps. Anisotropic models are studied by fitting two parameters, dark mass and velocity anisotropy, to the data. In this case all profiles yield good fits, but the steeper the cusp of the profile, the more tangential is the velocity distribution required to fit the data. To resolve this well-known degeneracy of density profile versus velocity anisotropy, we obtain predictions for the kurtosis of the line-of-sight velocity distribution for models found to provide best fits to the velocity dispersion profiles. It turns out that profiles with cores typically yield higher values of kurtosis which decrease more steeply with distance than the cuspy profiles, which will allow us to discriminate between the profiles once the kurtosis measurements become available. We also show that with present quality of the data the alternative explanation of velocity dispersions in terms of Modified Newtonian Dynamics cannot yet be ruled out.