发表机构
Yale University; Carnegie Institution for Science; University of Toronto; University of Virginia; Space Telescope Science Institute; Johns Hopkins University; University of Chicago; Fermi National Accelerator Laboratory（耶鲁大学; 卡内基科学研究所; 多伦多大学; 弗吉尼亚大学; 太空望远镜科学研究所; 约翰斯·霍普金斯大学; 芝加哥大学; 费米国家加速器实验室）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过多目标光谱观测，证认 Boötes V、Leo Minor I 和 DELVE 2 为超暗弱矮星系，并首次确认 DELVE 2 为 LMC 的长期束缚卫星，提出基于半光半径和表面亮度的分类判据。
AI 中文摘要
我们首次对 Boötes V、Leo Minor I 和 DELVE 2 进行了多目标光谱观测——这三个位于银河系外晕（日心距 71 kpc ≤ D_⊙ ≤ 102 kpc）中的小型（20 pc ≤ r_1/2 ≤ 26 pc）、超暗弱（-3.2 ≤ M_V ≤ -2.1）恒星系统，此前其分类尚不明确。利用针对每个卫星至少两个历元的 Keck/DEIMOS 或 Magellan/IMACS 观测，我们分别在三个系统中识别出 13、7 和 7 个光谱成员。我们初步测出 DELVE 2 的速度弥散 σ_v = 2.1^{+1.5}_{-0.9} km s^{-1}，但对 Boötes V 和 Leo Minor I 仅给出上限 σ_v < 2.7 km s^{-1} 和 σ_v < 7.8 km s^{-1}。我们发现这三个系统均非常贫金属，平均铁丰度 -2.85 ≤ [Fe/H] 平均值 ≤ -2.15。Boötes V 和 Leo Minor I 均显示出明确的金属丰度弥散（σ_[Fe/H] = 0.46^{+0.18}_{-0.12} dex 和 σ_[Fe/H] = 0.57^{+0.23}_{-0.18} dex），而 DELVE 2 在三颗恒星中显示出中等显著性的弥散（σ_[Fe/H] = 0.52^{+0.29}_{-0.25} dex）。主要基于这些金属丰度测量，我们 confidently 将 Boötes V 和 Leo Minor I 分类为矮星系，并确定 DELVE 2 也很可能是矮星系。我们在联合的银河系 + LMC 引力势中探索了每个卫星的轨道，首次证实 DELVE 2 是 LMC 的长期束缚卫星。最后，我们回顾了经验性的银河系卫星分类图景，发现几乎所有光谱表征的、方位角平均半光半径 r_1/2 > 15 pc 且表面亮度 μ_V,1/2 > 26.5 mag arcsec^{-2} 的卫星都可能是矮星系。这一结果可为 Rubin、Roman 和 Euclid 发现的卫星提供初始概率分类指导。
英文摘要
We present the first multi-object spectroscopy of Boötes V, Leo Minor I, and DELVE 2 -- three small (20 pc $\le r_{1/2}\le$ 26 pc), ultra-faint ($-3.2\le M_V\le-2.1$) stellar systems in the outer Galactic halo (71 kpc $\le D_\odot\le$ 102 kpc) with heretofore ambiguous classifications. Leveraging at least two epochs of Keck/DEIMOS or Magellan/IMACS observations targeting each satellite, we identify 13, 7, and 7 spectroscopic members in the three systems, respectively. We tentatively resolve a $σ_v=2.1^{+1.5}_{-0.9}$ km s$^{-1}$ velocity dispersion for DELVE 2 but place upper limits of $σ_v<2.7$ km s$^{-1}$ and $σ_v<7.8$ km s$^{-1}$ for Boötes V and Leo Minor I. We find that all three systems are very metal-poor, with mean iron abundances $-2.85\le\overline{\rm [Fe/H]}\le-2.15$. Both Boötes V and Leo Minor I display unambiguous metallicity spreads ($σ_{\rm [Fe/H]}=0.46^{+0.18}_{-0.12}$ dex and $σ_{\rm [Fe/H]}=0.57^{+0.23}_{-0.18}$ dex), while DELVE 2 displays a modestly significant spread ($σ_{\rm [Fe/H]}=0.52^{+0.29}_{-0.25}$ dex) across three stars. Based primarily on these metallicity measurements, we confidently classify Boötes V and Leo Minor I as dwarf galaxies and determine that DELVE 2 is most likely a dwarf galaxy as well. We explore the orbit of each satellite in a joint Milky Way + LMC potential, confirming for the first time that DELVE 2 is a long-term bound satellite of the LMC. Finally, we review the empirical Milky Way satellite classification landscape and find that nearly every spectroscopically characterized satellite with azimuthally averaged half-light radius $r_{1/2}>15$ pc and surface brightness $μ_{V,1/2}>26.5$ mag arcsec$^{-2}$ is likely a dwarf galaxy. This result can guide initial probabilistic classifications for satellites discovered by $\textit{Rubin}$, $\textit{Roman}$, and $\textit{Euclid}$.
Comments26 pages, 13 Figures, 6 tables. To be submitted to the Open Journal of Astrophysics. Member catalogs available on Zenodo: https://doi.org/10.5281/zenodo.23045325
