银河系高速云的距离。I. Cohen Stream、复杂GCP、云g1
Distances to Galactic high-velocity clouds. I. Cohen Stream, complex GCP, cloud g1
摘要：
高速和中速星际云（HVC/IVC）是银河系及其周围高能过程的示踪物。在圆盘上方约1 kpc的近太阳金属丰度的云追踪圆盘和晕（银河喷泉）之间的物质循环。麦哲伦流由从SMC中提取的气体潮汐组成，追踪银河系的暗物质潜力。其他几个HVC的金属丰度较低，似乎是在追踪不断下沉的星系际气体的吸积。这些断言得到了过去十年中测量的大约十片云的金属丰度（0.1到1个太阳）的支持。然而，直接测量到高压输电线的距离仍然难以实现。在本文中，我们提出了四个新的距离括号，使用星际\CaII H和K吸收遥远的星系晕星的VLT观测。我们推导出科恩流的距离括号为5.0至11.7千秒差距（可能是一个下降的低金属含量云），9.8至15.1 kpc的复杂GCP（也称为史密斯云或HVC 40 -15+100，起源仍然未知），IVC为1.0至2.7 kpc，似乎与英仙座臂中喷泉的回流有关，而云g1则为1.8至3.8千秒差距，它似乎处于喷泉的流出阶段。我们的测量进一步表明，银河系正在吸积大量的气态物质，这影响了银河系当前和未来的动力学和化学演化。
英文摘要：
The high- and intermediate-velocity interstellar clouds (HVCs/IVCs) are tracers of energetic processes in and around the Milky Way. Clouds with near-solar metallicity about one kpc above the disk trace the circulation of material between disk and halo (the Galactic Fountain). The Magellanic Stream consists of gas tidally extracted from the SMC, tracing the dark matter potential of the Milky Way. Several other HVCs have low-metallicity and appear to trace the continuing accretion of infalling intergalactic gas. These assertions are supported by the metallicities (0.1 to 1 solar) measured for about ten clouds in the past decade. Direct measurements of distances to HVCs have remained elusive, however. In this paper we present four new distance brackets, using VLT observations of interstellar \CaII H and K absorption toward distant Galactic halo stars. We derive distance brackets of 5.0 to 11.7 kpc for the Cohen Stream (likely to be an infalling low-metallicity cloud), 9.8 to 15.1 kpc for complex GCP (also known as the Smith Cloud or HVC40-15+100 and with still unknown origin), 1.0 to 2.7 kpc for an IVC that appears associated with the return flow of the Fountain in the Perseus Arm, and 1.8 to 3.8 kpc for cloud g1, which appears to be in the outflow phase of the Fountain. Our measurements further demonstrate that the Milky Way is accreting substantial amounts of gaseous material, which influences the Galaxy's current and future dynamical and chemical evolution.
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