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arXiv 0801.3682astro-ph
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高红移阻尼莱曼α系统中的分子氢：VLT/UVES数据库

Molecular hydrogen in high-redshift Damped Lyman-alpha systems: The VLT/UVES database

P. Noterdaeme, C. Ledoux, P. Petitjean, R. Srianand

备注：
11 pages, 1 table, 10 figures. Accepted for publication in A&A
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摘要：

本文介绍了利用ESO甚大望远镜（VLT）紫外和可见中阶梯摄谱仪（UVES）观测的高红移（1.8 < zabs <= 4.2）阻尼莱曼α系统（DLAs）中氢分子的研究现状。我们确定了77个DLAs/强亚DLAs，log N（HI）>= 20和z_abs > 1.8，其中包括红移的H2莱曼和/或维尔纳带吸收线的数据。以均匀方式进行的HI、H2和金属线测量的这个样本是我们先前样本（Ledoux等人，2003）的两倍多，并且考虑到迄今为止可以完成H2搜索的每个系统，包括所有未检测到的系统。在其中13个体系中检测到了H2，其分子分数在f= 5 × 10 ^-7和f=0.1之间，其中f=2N（H2）/（2N（H2）+N（HI））。测量其余64个系统的上限，检测限通常为log N（H2）=14.3，对应于log f<-5。我们发现，大约35%的DLA的金属丰度相对于太阳[X/H]>=-1.3（即，1/20太阳能），其中X = Zn、S或Si，具有分子分数log f>-4.5，而在其中的50%中检测到H2--与分子分数无关。相比之下，仅约4%的[X/H]<-1.3 DLAs have log f>-4.5。我们表明，H2的存在并不强烈地依赖于总中性氢柱密度，虽然发现log f&gt;-4.5的概率是更高的log N（HI）&gt;=20.8比低于此限制（分别为19%和7%）。在对大N（HI）的轻微偏差进行校正后，发现log N（HI）&gt;=20 DLA中的总体H2检测率为约16%（仅考虑log f&gt;-4.5检测为10%）。[截短]

英文摘要：

We present the current status of ongoing searches for molecular hydrogen in high-redshift (1.8 < zabs <= 4.2) Damped Lyman-alpha systems (DLAs) capitalising on observations performed with the ESO Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). We identify 77 DLAs/strong sub-DLAs, with log N(HI) >= 20 and z_abs > 1.8, which have data that include redshifted H2 Lyman and/or Werner-band absorption lines. This sample of HI, H2 and metal line measurements, performed in an homogeneous manner, is more than twice as large as our previous sample (Ledoux et al. 2003) and considers every system in which searches for H2 could be completed so far, including all non-detections. H2 is detected in thirteen of the systems with molecular fractions of values between f=5x10^-7 and f=0.1, where f=2N(H2)/(2N(H2)+N(HI)). Upper limits are measured for the remaining 64 systems with detection limits of typically log N(H2)=14.3, corresponding to log f<-5. We find that about 35% of the DLAs with metallicities relative to solar [X/H]>=-1.3 (i.e., 1/20th solar), with X = Zn, S or Si, have molecular fractions log f>-4.5, while H2 is detected -- regardless of the molecular fraction -- in 50% of them. In contrast, only about 4% of the [X/H]<-1.3 DLAs have log f>-4.5. We show that the presence of H2 does not strongly depend on the total neutral hydrogen column density, although the probability of finding log f>-4.5 is higher for log N(HI)>=20.8 than below this limit (19% and 7% respectively). The overall H2 detection rate in log N(HI)>=20 DLAs is found to be about 16% (10% considering only log f>-4.5 detections) after correction for a slight bias towards large N(HI). [truncated]

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