Leo T is a gas-rich dwarf located at |$414\, {\rm kpc}$| (1.4R_vir) distance from the Milky Way (MW) and it is currently assumed to be on its first approach. Here, we present an analysis of orbits calculated backwards in time for the dwarf with our new code delorean, exploring a range of systematic uncertainties, e.g. MW virial mass and accretion, M31 potential, and cosmic expansion. We discover that orbits with tangential velocities in the Galactic standard-of-rest frame lower than |$| \vec{u}_{\rm t}^{\rm GSR}| \le 63^{+47}_{-39}\, {\rm km}\, {\rm s}^{\rm -1}$| result in backsplash solutions, i.e. orbits that entered and left the MW dark matter halo in the past, and that velocities above |$| \vec{u}_{\rm t}^{\rm GSR}| \ge 21^{+33}_{-21}\, {\rm km}\, {\rm s}^{\rm -1}$| result in wide-orbit backsplash solutions with a minimum pericentre range of |$D_{\rm min} \ge 38^{+26}_{-16}\, {\rm kpc}$|⁠, which would allow this satellite to survive gas stripping and tidal disruption. Moreover, new proper motion estimates overlap with our orbital solution regions. We applied our method to other distant MW satellites, finding a range of gas stripped backsplash solutions for the gasless Cetus and Eridanus II, providing a possible explanation for their lack of cold gas, while only first infall solutions are found for the H i-rich Phoenix I. We also find that the cosmic expansion can delay their first pericentre passage when compared to the non-expanding scenario. This study explores the provenance of these distant dwarfs and provides constraints on the environmental and internal processes that shaped their evolution and current properties.

中文翻译：

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银河系光环外缘中的矮人：第一颗落入卫星还是后飞溅卫星？

Leo T 是一个富含气体的矮星，位于 |$414\, {\rm kpc}$| (1.4R_vir) 距银河系 (MW) 的距离，目前假定它处于第一种接近状态。在这里，我们使用我们的新代码 delorean 对矮人的轨道进行了时间向后计算的分析，探索了一系列系统不确定性，例如 MW 维里质量和吸积、M31 势能和宇宙膨胀。我们发现在银河静止标准坐标系中切线速度低于 |$| 的轨道 \vec{u}_{\rm t}^{\rm GSR}| \le 63^{+47}_{-39}\, {\rm km}\, {\rm s}^{\rm -1}$| 导致反溅解，即过去进入和离开 MW 暗物质晕的轨道，以及高于 |$| 的速度。\vec{u}_{\rm t}^{\rm GSR}| \ge 21^{+33}_{-21}\, {\rm km}\, {\rm s}^{\rm -1}$| 导致宽轨道后挡板解决方案的最小周向范围为 |$D_{\rm min} \ge 38^{+26}_{-16}\, {\rm kpc}$|⁠，这将允许这颗卫星在气体剥离和潮汐破坏中幸存下来。此外，新的自行估计与我们的轨道解区域重叠。我们将我们的方法应用于其他遥远的 MW 卫星，为无气体的 Cetus 和 Eridanus II 找到了一系列气体剥离后飞溅的解决方案，为它们缺乏冷气体提供了可能的解释，而对于富含 H i Phoenix I。我们还发现，与非膨胀场景相比，宇宙膨胀可以延迟它们的第一次中心通过。