标题： 银河系晕中的中间速度云分子氢的FUSE调查 显示英文标题

标题： A FUSE Survey of Molecular Hydrogen in Intermediate-Velocity Clouds in the Milky Way Halo

摘要： 远紫外线光谱探测器（FUSE）数据用于研究银河系低晕中中间速度云（IVCs）中的分子氢（H_2）含量。 我们分析了56个（主要是河外的）背景源的星际吸收，以研究在61个IVC组分中Lyman-和Werner带的H_2吸收，这些组分的H I柱密度大于10^19 cm^-2。 对于信噪比好的数据（每分辨率单元约9以上），在14种情况下成功检测到IVC气体中的H_2，其柱密度在约10^14至约10^17 cm^-2之间。 我们在FUSE光谱中发现另外17个可能的IVC H_2检测结果，这些光谱的信噪比较低。 分子氢分数f在10^-6至10^-3之间，这意味着这些云中存在致密且主要为中性气体相，很可能与这些云中的冷中性介质（CNM）有关。 如果H_2保持在形成-解离平衡中，这些云中的CNM可以通过紧凑（D~0.1 pc）丝状结构来表征，体积密度约为n_H~30 cm^-3。 IVC气体中H_2的相对较高的检测率表明，这些云中的CNM是普遍存在的。 可能存在密度更高、分子分数更高的区域，但由于它们尺寸较小，在吸收中检测它们会很困难。 显示英文摘要

摘要： Far Ultraviolet Spectroscopic Explorer (FUSE) data is used to investigate the molecular hydrogen (H_2) content of intermediate-velocity clouds (IVCs) in the lower halo of the Milky Way. We analyze interstellar absorption towards 56 (mostly extragalactic) background sources to study H_2 absorption in the Lyman- and Werner bands in 61 IVC components at H I column densities >10^19 cm^-2. For data with good S/N (~9 per resolution element and higher), H_2 in IVC gas is convincingly detected in 14 cases at column densities varying between ~10^14 and ~10^17 cm^-2. We find an additional 17 possible H_2 detections in IVCs in FUSE spectra with lower S/N. The molecular hydrogen fractions, f, vary between 10^-6 and 10^-3, implying a dense, mostly neutral gas phase that is probably related to the Cold Neutral Medium (CNM) in these clouds. If the H_2 stays in formation-dissociation equlibrium, the CNM in these clouds can be characterized by compact (D~0.1 pc) filaments with volume densities on the order of n_H~30 cm^-3. The relatively high detection rate of H_2 in IVC gas implies that the CNM in these clouds is ubiquitous. More dense regions with much higher molecular fractions may exist, but it would be difficult to detect them in absorption because of their small size.