利用M68星流与DESI光谱数据改进对银河系引力势的约束
Improved constraints on the Milky Way potential using the M68 stream and DESI spectroscopic data
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中文总结 AI 辅助
该研究结合DESI光谱数据与M68星流样本，改进了银河系引力势约束，得到盘质量、暗物质晕轴比及M68日心距离的精确结果。
中文摘要 AI 辅助
我们选取了属于球状星团M68（NGC 4590，又称Fjörm）恒星流的恒星样本。该样本相较于仅使用盖亚（Gaia）数据的前期样本有所改进，因为它纳入了暗能量光谱仪（DESI）巡天的光谱测量数据以及DESI遗产巡天的测光数据。该样本包含96颗恒星，每颗恒星都拥有来自盖亚DR3的五个相空间参数和来自DESI的视向速度，覆盖了该星流的整个观测段，是迄今为止拥有测量视向速度的最大规模M68星流恒星样本。观测到的星流比N体模拟所预期的更宽，且距离星流中心最远的恒星在视向速度空间中呈现相关性，这表明这些恒星不可能是在静态轴对称引力势中从星团剥离的。通过对利用N体模拟生成的星流恒星 mock 样本进行建模，我们发现可以可靠地约束银河系的盘质量$M_{\rm d}$和暗物质晕轴比$q_{\rm h}$，原因是该星流靠近盘且几乎与盘平行。利用44颗与从星团剥离相符的恒星，结合银河系旋转曲线的测量数据，我们对银河系引力势进行了约束，得到$M_{\rm d} = 5.34 \times 10^{10} \text{M}_{\rm sun} \text{±} 0.57 \times 10^{10} \text{M}_{\rm sun}$，以及扁球形晕的$q_{\rm h} = 0.83^{+0.06}_{-0.05}$。此外，通过拟合星流轨迹，我们估计M68的日心距离为$r=10.55\boxed{±}0.09$ kpc。
英文摘要
We present a selection of stars belonging to the stellar stream of the M68 (NGC 4590) globular cluster, also known as Fjörm. This star selection is an improvement on previous ones that used only Gaia data, as it incorporates spectroscopic measurements from the DESI survey and photometric data from the DESI Legacy Surveys. The selection contains 96 stars, each with five phase-space parameters from Gaia-DR3 and radial velocity from DESI, covering the entire observed section of the stream. This constitutes the largest selection of M68 stream stars with measured radial velocities to date. The observed stream is wider than expected from N-body simulations, and the stars farthest from the centre of the stream appear to be correlated in radial velocity space. This suggests that these stars cannot have been stripped from the cluster in a static axisymmetric potential. By modelling a mock sample of stream stars created using an N-body simulation, we found that we could reliably constrain the disc mass $M_{\rm d}$ and the dark matter halo axis ratio $q_{\rm h}$ of the Milky Way. This is because the stream flows close to and almost parallel to the disc. Using the 44 stars that are consistent with having been stripped from the cluster, combined with measurements of the Milky Way's rotation curve, we constrain the Galactic potential, obtaining $M_{\rm d} = 5.34 \pm 0.57 \times 10^{10}$ M$_{\rm sun}$ and an oblate halo of $q_{\rm h} = 0.83^{+0.06}_{-0.05}$. Additionally, by fitting the stream track, we estimate the Heliocentric distance of M68 to be $r=10.55\pm0.09$ kpc.
