论文标题
Grus I的麦哲伦/iMacs光谱：低金属性超生物矮星系
Magellan/IMACS spectroscopy of Grus I: A low metallicity ultra-faint dwarf galaxy
论文作者
论文摘要
我们提出了一项从中分辨率（$ r \ sim11,000 $）麦哲伦/iMacs Spectra的Grus I超生物Dwarf Galaxy（UFD）的化学动力学研究。我们根据其低金属性和相干径向速度确定了八个确认的GRUS成员，以及仅得出速度的四名候选成员。与以前的工作相反，我们发现Grus i具有$ \ langle $ [fe/h] $ \ rangle = -2.62 \ pm 0.11 $ dex的非常低的金属性，使其成为最贫穷的UFD。格鲁斯一世的系统性径向速度为$ -143.5 \ pm1.2 $ km s $ s $^{ - 1} $，速度分散$σ_{\ text {rv}} = 2.5^{+1.3} {+1.3} _ { - 0.8} _ { - 0.8} $ km s $ s $ s $ s $ 1} （r_h）= 8^{+12} _ { - 4} \ times 10^5 $ m $ _ {\ odot} $，质量比为m/l $ _v $ = $ _V $ = $ 440^{+650} _ { - 250} _ { - 250} $ _ \ odot $ _ \ odot $/l $/l $/l $ _ \ odot $在动态平衡的假设下，我们的分析证实了Grus I是一个以深色为主导的UFD（M/L $> 80 $ M $ _ \ odot $/l $ _ \ odot $）。但是，我们无法解析金属性分散（$σ_ {\ text {[fe/h]}}} <0.44 $ dex）。我们的结果表明，GRUS I是一个相当典型的UFD，其参数与微弱星系的质量金属性和金属性稀疏度趋势一致。该协议表明，格鲁斯一世并未因其轨道参数而以银河系的潮汐相遇而损失了特别重要的质量。有趣的是，Grus I具有最低的中央密度（$ρ_{1/2} \ sim 3.5 _ { - 2.1}^{+5.7} \ times 10^7 $ m $ m $ m $ m $ _ \ odot $ kpc $^{ - 3} $）的UFDS，这些UFDS尚未涉及。除了这些遗物星系外部地区的任何多样性外，UFD的形成和演变模型还需要解释这些中心密度的多样性。
We present a chemodynamical study of the Grus I ultra-faint dwarf galaxy (UFD) from medium-resolution ($R\sim11,000$) Magellan/IMACS spectra of its individual member stars. We identify eight confirmed members of Grus I, based on their low metallicities and coherent radial velocities, and four candidate members for which only velocities are derived. In contrast to previous work, we find that Grus I has a very low mean metallicity of $\langle$[Fe/H]$\rangle = -2.62 \pm 0.11$ dex, making it one of the most metal-poor UFDs. Grus I has a systemic radial velocity of $-143.5\pm1.2$ km s$^{-1}$ and a velocity dispersion of $σ_{\text{rv}} = 2.5^{+1.3}_{-0.8}$ km s$^{-1}$ which results in a dynamical mass of $M_{1/2} (r_h) = 8^{+12}_{-4} \times 10^5$ M$_{\odot}$ and a mass-to-light ratio of M/L$_V$ = $440^{+650}_{-250}$ M$_\odot$/L$_\odot$. Under the assumption of dynamical equilibrium, our analysis confirms that Grus I is a dark-matter-dominated UFD (M/L $> 80$ M$_\odot$/L$_\odot$). However, we do not resolve a metallicity dispersion ($σ_{\text{[Fe/H]}} < 0.44$ dex). Our results indicate that Grus I is a fairly typical UFD with parameters that agree with mass-metallicity and metallicity-luminosity trends for faint galaxies. This agreement suggests that Grus I has not lost an especially significant amount of mass from tidal encounters with the Milky Way, in line with its orbital parameters. Intriguingly, Grus I has among the lowest central density ($ρ_{1/2} \sim 3.5_{-2.1}^{+5.7} \times 10^7$ M$_\odot$ kpc$^{-3}$) of the UFDs that are not known to be tidally disrupting. Models of the formation and evolution of UFDs will need to explain the diversity of these central densities, in addition to any diversity in the outer regions of these relic galaxies.
