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arXiv 2407.21790astro-ph.GA
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银河系内暗物质晕三轴性的首次测量

First measurement of the triaxiality of the inner dark matter halo of the Milky Way

Hanneke C. Woudenberg, Amina Helmi

备注：
submitted to A&A, comments welcome
发表信息：
A&A 691, A277 (2024)
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AI总结：

本文利用 Gaia DR3 数据研究 Helmi Streams 的相空间结构，首次精确测量了银河系内暗物质晕的三轴性，并揭示轨道共振驱动了恒星流团块的形成与不同混合程度。

摘要：

恒星流是星系质量分布特别敏感的探针。在这项工作中，我们聚焦于 Helmi Streams，这是一个被吸积的矮星系围绕银河系内部运行的遗迹。我们深入研究了它们特殊的动力学性质，并利用这些性质对银河系势场，特别是其内部 20 kpc 范围内的暗物质晕，提供严格的约束。我们从 Gaia DR3 中提取了 Helmi Streams 的 6D 相空间信息，并确认这些恒星流在角动量空间中分裂成两个团块，且这两个团块表现出不同程度的相混合。为了解释这些特征，我们探索了一系列具有三轴 NFW 晕的银河系势场模型，并进一步受到旋转曲线数据的约束。我们发现，一个具有轻度三轴暗物质晕的银河系势场，其参数为 $p=1.013^{+0.006}_{-0.006}$，$q=1.204^{+0.032}_{-0.036}$，$M_{\rm{discs}}=4.65^{+0.47}_{-0.57}\cdot10^{10} M_{\odot}$ 以及 $M_{\rm{DM}}(< 15 \text{kpc})=1.14^{+0.11}_{-0.10}\cdot10^{11} M_{\odot}$，是随着时间在角动量空间中形成两个团块所必需的。它们的形成是由这些团块处于不同的轨道族并且接近一个轨道共振这一事实所驱动的。该共振也解释了所观测到的不同程度的混合，以及一个动力学冷子团块（也称为 S2）的存在。这次对银河系内部暗物质晕三轴性的首次且非常精确的测量，独特地揭示了相混合恒星流对引力势场精确形式的高度敏感性。

英文摘要：

Stellar streams are particularly sensitive probes of the mass distribution of galaxies. In this work, we focus on the Helmi Streams, the remnants of an accreted dwarf galaxy orbiting the inner Milky Way. We examine in depth their peculiar dynamical properties, and use these to provide tight constraints on the Galactic potential, and specifically on its dark matter halo in the inner 20 kpc. We extract 6D phase-space information for the Helmi Streams from Gaia DR3, and confirm that the Streams split up into two clumps in angular momentum space, and that these depict different degrees of phase-mixing. To explain these characteristics we explore a range of Galactic potential models with a triaxial NFW halo, further constrained by rotation curve data. We find that a Galactic potential with a mildly triaxial dark matter halo, having $p=1.013^{+0.006}_{-0.006}$, $q=1.204^{+0.032}_{-0.036}$, $M_{\rm{discs}}=4.65^{+0.47}_{-0.57}\cdot10^{10} M_{\odot}$ and $M_{\rm{DM}}(< 15 \text{kpc})=1.14^{+0.11}_{-0.10}\cdot10^{11} M_{\odot}$, is required to form two clumps in angular momentum space over time. Their formation is driven by the fact that the clumps are on different orbital families and close to an orbital resonance. This resonance also explains the different degrees of mixing observed, as well as the presence of a dynamically cold subclump (also known as S2). This first and very precise measurement of the triaxiality of the inner dark matter halo of the Galaxy uniquely reveals the high sensitivity of phase-mixed streams to the exact form of the gravitational potential.

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