论文标题
NGC 3201，M68和Palomar 5的恒星溪流中的银河系暗物质光环的底色
The oblateness of the Milky Way dark matter halo from the stellar streams of NGC 3201, M68, and Palomar 5
论文作者
论文摘要
我们使用来自球状簇NGC 3201，M68和Palomar 5的三个恒星流对银河系暗物质裸露的限制进行了限制。先前对恒星种群动力平衡的重力势和远距离乳头卫星的限制。我们将深色光环建模为轴对称，轴比$q_ρ^{\ rm h} $，以及两个两个幂律密度剖面的附加自由参数。晕轴轴比几乎没有受到NGC 3201流的约束，但必须通过Palomar 5的流接近球形（$q_ρ^{\ rm h} = 1.01 \ pm0.09 $）和m68（$q_ρ^{$q_ρ^{\ rm H} = 1.14^$ 0.14^$ 0.21}允许更加厚的形状。这三个流在一起装有光轴比率$q_ρ^{\ rm h} = 1.06 \ pm0.06 $和core radius $ \ sim $ 20 kpc。我们对光环形状的估计与先前使用其他观察数据的研究一致，并且与宇宙学模拟有张力，预测大多数螺旋星系都将暗物质置换剂与垂直于光盘的短轴相结合。我们讨论了为什么麦哲伦云的影响太小，无法改变我们对光环轴比的结论。我们注意到，在扁盘电势中球形光环的动态平衡意味着沿垂直方向比水平方向大的各向异性暗物质速度散布率更大，这应该与银河系的组装历史有关。
We explore constraints on the Milky Way dark matter halo oblateness using three stellar streams from globular clusters NGC 3201, M68, and Palomar 5. Previous constraints on the gravitational potential from dynamical equilibrium of stellar populations and distant Milky Way satellites are included. We model the dark halo as axisymmetric with axis ratio $q_ρ^{\rm h}$ and four additional free parameters of a two power-law density profile. The halo axis ratio, while barely constrained by the NGC 3201 stream alone, is required to be close to spherical by the streams of Palomar 5 ($q_ρ^{\rm h}=1.01\pm0.09$) and M68 ($q_ρ^{\rm h}=1.14^{+0.21}_{-0.14}$), the latter allowing a more prolate shape. The three streams together are well fitted with a halo axis ratio $q_ρ^{\rm h}=1.06\pm0.06$ and core radius $\sim$ 20 kpc. Our estimate of the halo shape agrees with previous studies using other observational data and is in tension with cosmological simulations predicting that most spiral galaxies have oblate dark matter halos with the short axis perpendicular to the disc. We discuss why the impact of the Magellanic Clouds tide is too small to change our conclusion on the halo axis ratio. We note that dynamical equilibrium of a spherical halo in the oblate disk potential implies an anisotropic dark matter velocity dispersion, larger along the vertical direction than the horizontal ones, which should relate to the assembly history of the Milky Way.
