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arXiv 2505.04475astro-ph.GA
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仙女座矮星系的质量建模：仙女座VI与仙女座XXIII

Mass Modeling the Andromeda Dwarf Galaxies: Andromeda VI and Andromeda XXIII

Connor S. Pickett, Michelle L. M. Collins, R. Michael Rich, Justin I. Read, Emily J. E. Charles, Nicolas Martin, Scott Chapman, Alan McConnachie, Alessandro Savino, Daniel R. Weisz

备注：
19 pages, 16 figures. Accepted to MNRAS
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AI总结：

本研究对仙女座的两个矮星系And VI和And XXIII开展动力学质量建模，测定了其包围质量、质光比与暗物质密度，发现前者呈暗物质尖点分布、后者密度偏低，为理解暗物质本质和本星系群矮星系演化提供了新观测约束。

摘要：

精确绘制低质量矮椭球星系（dSph）的质量分布剖面，能够帮助我们检验暗物质（DM）模型的预测。截至目前，这类分析主要针对银河系（MW）的卫星星系开展。与此同时，仙女座星系（M31）拥有35个已知矮星系，但迄今仅有两个完成了成功的质量建模。为更好地理解暗物质的本质，有必要对本星系群的矮星系开展更全面的研究。在本研究中，我们对两个光度较高的仙女座矮星系——仙女座VI（And VI）和仙女座XXIII（And XXIII）开展了动力学研究。我们推算得到And VI的包围质量为M(r < rₕ) = (4.9 ± 1.5) × 10⁷ M⊙，对应的质光比为[M/L]ᵣₕ = (27.1 ± 8.2) M⊙/L⊙。我们推算得到And XXIII的包围质量为M(r < rₕ) = (3.1 ± 1.9) × 10⁷ M⊙，对应的质光比为[M/L]ᵣₕ = (90.2 ± 53.9) M⊙/L⊙。我们使用动力学Jeans建模工具gravsphere，测定了And VI和And XXIII在150秒差距处的暗物质密度，得到ρ_DM,VI(150 pc) = (1.4 ± 0.5) × 10⁸ M⊙ kpc⁻³，ρ_DM,XXIII(150 pc) = 0.5₋₀.₃⁺⁰.⁴ × 10⁸ M⊙ kpc⁻³。我们的结果表明，And VI是首个被证实处于尖点分布状态的M31卫星星系。And XXIII的密度更低，这意味着其中心暗物质密度可能更呈核状分布，或是因潮汐作用导致密度降低。这一发现让And XXIII加入了数量不断增多的M31矮星系行列——这类星系的中心密度低于大多数银河系矮星系，也低于标准宇宙学模型中孤立矮星系的预期值。这一现象或许可以解释为：M31的矮星系比银河系的同类矮星系经历了更强的潮汐作用。

英文摘要：

Accurately mapping the mass profiles of low mass dwarf spheroidal (dSph) galaxies allows us to test predictions made by dark matter (DM) models. To date, such analyses have primarily been performed on Milky Way (MW) satellites. Meanwhile, the Andromeda Galaxy (M31) is home to 35 known dwarf galaxies, yet only two have been successfully mass-modeled so far. A more comprehensive study of Local Group dwarfs is necessary to better understand the nature of dark matter. In this study, we have undertaken a dynamical study of two higher-luminosity Andromeda dwarf galaxies: Andromeda VI (And VI) and Andromeda XXIII (And XXIII). We infer an enclosed mass for And VI of M(r $<$ r$_{h}$) = (4.9 $\pm$ 1.5) $\times$ 10$^{7}$ M$_{\odot}$, corresponding to a mass-to-light ratio of $[M/L]_{r_{\rm{h}}}$ = (27.1 $\pm$ 8.2) M$_{\odot}$/L$_{\odot}$. We infer an enclosed mass for And XXIII of M(r $<$ r$_{h}$) = (3.1 $\pm$ 1.9) $\times$ 10$^{7}$ M$_{\odot}$, corresponding to a mass-to-light ratio of $[M/L]_{r_{\rm{h}}}$ = (90.2 $\pm$ 53.9) M$_{\odot}$/L$_{\odot}$. Using the dynamical Jeans modeling tool, \gravsphere, we determine And VI and And XXIII's dark matter density at 150 pc, finding $ρ_{\rm{DM,VI}}$(150 pc) = (1.4 $\pm$ 0.5) $\times 10^{8}$ M$_{\odot}$ kpc$^{-3}$ and $ρ_{\rm{DM,XXIII}}$(150 pc) = 0.5$\substack{+0.4 \\ -0.3} \times 10^{8}$ M$_{\odot}$ kpc$^{-3}$. Our results make And VI the first mass-modeled M31 satellite to fall into the cuspy regime. And XXIII has a lower density, implying either a more cored central dark matter density, or a lowering of the density through tides. This adds And XXIII to a growing list of M31 dwarfs with a central density lower than most MW dwarfs and lower than expected for isolated dwarfs in the Standard Cosmology. This could be explained by the M31 dwarfs having experienced stronger tides than their MW counterparts.

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