标题： HE 0515-4414方向z=1.15处的分子氢探测 显示英文标题

标题： Detection of molecular hydrogen at z=1.15 toward HE 0515-4414

摘要： 在一个红移 \(z=1.15\) 的亮类星体 HE0515-4414（\(zem = 1.71\)）方向上发现了一个新的分子氢云，该云位于次饱和 Lyα 吸收体 [log N(HI)=19.88±0.05] 中。 利用哈勃太空望远镜上的空间望远镜成像光谱仪 (STIS)，在这颗类星体的紫外光谱中识别出了超过 30 条 Lyman 带系中的 H2 吸收特征。 含 H2 的云表现出总 H2 柱密度 \(N(\text\{H\}_2) = (8.7^\{{+8.7}\}_\{-{4.0}\}) \times 10^\{16\} \, \text\{cm\}^\{-2\}\)，以及从基态电子振动状态的 J=0-5 转动能级产生的 H2 线计算得出的分数分子丰度 \(f(\text\{H\}_2) = (2.3^\{{+2.3}\}_\{\,{-1.1}\}) \times 10^\{-3\}\)。 在云边缘估计的光解离率 \(I_0 \leq 1.8 \times 10^\{\text\{{-8}\}\} \, \text\{s\}^\{-1\}\) 远高于银河盘的平均值 \(I_\{\text\{MW\}\} \sim 5.5 \times 10^\{\text\{{-11}\}\} \, \text\{s\}^\{-1\}\)。 这可能表明在 \(z=1.15\) 系统中的恒星形成活动比在 \(z \sim 3\) 的分子云中更为活跃，在那里 \(I \sim I_\{\text\{MW\}\}\)。 我们还找到了一个初步证据，表明在 \(z=1.15\) 处 H2 在尘埃表面的形成速率系数比经典的银河系值大一个数量级，即 \(R_\{\text\{MW\}\} \sim 3 \times 10^\{-17\} \, \text\{cm\}^3 \, \text\{s\}^\{-1\}\)。 根据 [Cr/Zn] 比估算出的相对尘埃-气体比例 \(k = 0.89 \pm 0.19\)（以银河盘平均值为单位），与该系统中的高分子分数相一致。 视线长度的估计值 \(L \sim 0.25 \, \text\{pc\}\) 可能意味着 H2 被限制在嵌入更稀薄气体中的小而密集的丝状结构中，这些丝状结构形成了 \(z=1.15\) 的次饱和 Lyα 吸收体。 显示英文摘要

摘要： A new molecular hydrogen cloud is found in the sub-damped Ly-alpha absorber [log N(HI)=19.88+/-0.05] at the redshift z=1.15 toward the bright quasar HE0515-4414 (zem = 1.71). More than 30 absorption features in the Lyman band system of H2 are identified in the UV spectrum of this quasar obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. The H2-bearing cloud shows a total H2 column density N(H2)=(8.7^{+8.7}_-{4.0}) 10^16 cm^-2, and a fractional molecular abundance f(H2)=(2.3^{+2.3}_{-1.1}) 10^-3 derived from the H2 lines arising from the J=0-5 rotational levels of the ground electronic vibrational state. The estimated rate of photodissociation at the cloud edge I_0<=1.8 10^{-8} s^-1 is much higher than the mean Galactic disk value, I_MW~=5.5 10^{-11} s^-1. This may indicate an enhanced star-formation activity in the z=1.15 system as compared with molecular clouds at z~=3 where I~=I_MW. We also find a tentative evidence that the formation rate coefficient of H2 upon grain surfaces at z=1.15 is a factor of 10 larger than a canonical Milky Way value, R_MW~=3 10^-17 cm^3 s^-1. The relative dust-to-gas ratio estimated from the [Cr/Zn] ratio is equal to k=0.89+/-0.19 (in units of the mean Galactic disk value), which is in good agreement with a high molecular fraction in this system. The estimated line-of-sight size of L~=0.25 pc may imply that the H2 is confined within small and dense filaments embedded in a more rarefied gas giving rise to the z=1.15 sub-damped Ly-alpha absorber.