论文标题
外银色方式上方的高速云层
The high-velocity clouds above the disk of the outer Milky Way: misty precipitating gas in a region roiled by stellar streams
论文作者
论文摘要
外部银河系的高速云（HVC）以$ 20^{\ circ} <l <190^{\ circ} $具有相似的空间位置，金属性和运动学学。此外，他们的位置和运动学与几个外推恒流相吻合。 HVC的起源可以连接到恒星流，要么直接从它们中剥离，要么由该地区的骨料祖细胞的骨料动态滚动沉淀。本文表明，根据以下观察结果，这些HVC在流中醒来时是“雾化”的降水。 QSO H1821+643的新的高分辨率（2.6 km/s）紫外线光谱法可以解决似乎是单个HVC吸收云（7 km/s的分辨率）成五个组件，分成$ t \ lisssim 3 \ lyssim 3 \ lysSim 3 \ times times 10^{4} $ k。和模型的归化度允许大量的金属性。高电离吸收线（SIIV，CIV和OVI）在运动学上与较低的离子化线对齐，并且不能轻易用光电离或平衡碰撞电离来解释；这些线最好与非平衡快速冷却模型相匹配，即具有高金属性和相当大量的HI的冷凝/沉淀气体。低电气化阶段的冷却时间比自由度时间和冷却时间与发声时间的比率较低，从而使碎片化和沉淀。 H1821+643的结果通过附近六个靶标的光谱进行了证实，这些目标同样显示了运动学相关的低和高电源吸收系线，并具有尘埃耗竭和快速冷却的证据。
The high-velocity clouds (HVCs) in the outer Milky Way at $20^{\circ} < l < 190^{\circ}$ have similar spatial locations, metallicities, and kinematics. Moreover, their locations and kinematics are coincident with several extraplanar stellar streams. The HVC origins may be connected to the stellar streams, either stripped directly from them or precipitated by the aggregate dynamical roiling of the region by the stream progenitors. This paper suggests that these HVCs are "misty" precipitation in the stream wakes based on the following observations. New high-resolution (2.6 km/s) ultraviolet spectroscopy of the QSO H1821+643 resolves what appears to be a single HVC absorption cloud (at 7 km/s resolution) into five components with $T \lesssim 3\times 10^{4}$ K. Photoionization models can explain the low-ionization components but require some depletion of refractory elements by dust, and model degeneracies allow a large range of metallicity. High-ionization absorption lines (SiIV, CIV, and OVI) are kinematically aligned with the lower-ionization lines and cannot be easily explained with photoionization or equilibrium collisional ionization; these lines are best matched by non-equilibrium rapidly cooling models, i.e., condensing/precipitating gas, with high metallicity and a significant amount of HI. Both the low- and high-ionization phases have low ratios of cooling time to freefall time and cooling time to sound-crossing time, which enables fragmentation and precipitation. The H1821+643 results are corroborated by spectroscopy of six other nearby targets that likewise show kinematically correlated low- and high-ionization absorption lines with evidence of dust depletion and rapid cooling.
