标题： FUSE对高纬度AGN的星际分子氢的调查 显示英文标题

标题： A FUSE Survey of Interstellar Molecular Hydrogen toward High-Latitude AGN

摘要： 我们报告了对银河系内分子氢（H2）在45条视线方向上的FUSE调查结果，这些方向指向高银纬的AGN（|b| > 20度）。 大多数（45条中的39条）视线显示出从Lyman和Werner带（1000至1126 A）之间的可检测银河系H2吸收，柱密度范围为 N(H2) = 10^(14.17-19.82) cm^-2。 在银河系北半球，我们识别出许多低柱密度区域，N(H2) < 10^15 cm^-2，经度l = 60-180度且银纬b > 54度。 这些“H2空洞”为河外紫外光谱学提供了宝贵的、无污染的视线，并且其中一些可能与“北烟囱”（低Na I吸收）和“Lockman Hole”（低N(HI)）有关。 将高银纬H2与139条OB星视线在银河系盘中的调查进行比较，表明高银纬和盘中H2云可能有不同的加热、冷却和紫外激发速率。 对于旋转态J = 0和1，高银纬的平均激发温度，<T_01(high)> = 124 +/- 8 K，略高于银河系盘中的<T_01(disk)> = 86 +/- 20 K。对于J = 2-4，<T_exc> = 498 +/- 28 K，柱密度比值，N(3)/N(1)，N(4)/N(1)，和N(4)/N(2)，表明在N(H2) > 10^18的视线中，盘和低晕中的紫外激发程度相当。 高银纬分子分数的分布显示，在较低总氢柱密度时发生转变，log N_H = 20.38 +/- 0.13，比银河系盘中的log N_H(disk) = 20.7更低。 如果盘和低晕中的远紫外辐射场相似，这表明在高密度、压缩云中H2形成率增强（由尘埃催化），这可能以高银纬、片状红外云的形式被探测到。 显示英文摘要

摘要： We report results from a FUSE survey of interstellar molecular hydrogen (H2) along 45 sight lines to AGN at high Galactic latitudes (|b| > 20 degrees). Most (39 of 45) of the sight lines show detectable Galactic H2 absorption from Lyman and Werner bands between 1000 and 1126 A, with column densities ranging from N(H2) = 10^(14.17-19.82) cm^-2. In the northern Galactic hemisphere, we identify many regions of low column, N(H2) < 10^15 cm^-2, between longitude l = 60-180 degrees and at b > 54 degrees. These `"H2 holes" provide valuable, uncontaminated sight lines for extragalactic UV spectroscopy, and a few may be related to the "Northern Chimney" (low Na I absorption) and "Lockman Hole" with low N(HI). A comparison of high-latitude H2 with 139 OB-star sight lines surveyed in the Galactic disk suggests that high-latitude and disk H2 clouds may have different rates of heating, cooling, and UV excitation. For rotational states J = 0 and 1, the mean excitation temperature at high latitude, <T_01(high)> = 124 +/- 8 K, is somewhat above that in the Galactic disk, <T_01(disk)> = 86 +/- 20 K. For J = 2-4, the <T_exc> = 498 +/- 28 K, and the column-density ratios, N(3)/N(1), N(4)/N(0), and N(4)/N(2), indicate a comparable degree of UV excitation in the disk and low halo for sight lines with N(H2) > 10^18. The distribution of molecular fractions at high latitude shows a transition at lower total hydrogen column density, log N_H = 20.38 +/- 0.13, than in the Galactic disk, log N_H(disk) = 20.7. If the FUV radiation fields are similar in disk and low halo, this suggests an enhanced (dust-catalyzed) H2 formation rate in higher-density, compressed clouds, which could be detectable as high-latitude, sheetlike infrared cirrus.