Spotting high-z molecular absorbers using neutral carbon Results from a complete spectroscopic survey with the VLT
Spotting high-z molecular absorbers using neutral carbon Results from a complete spectroscopic survey with the VLT
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DOI：
10.1051/0004-6361/201732266
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发表时间：
2018-04-24
影响因子：
6.5
通讯作者：
Lopez, S.
中科院分区：
文献类型：
--
作者：
Noterdaeme, P.;Ledoux, C.;Lopez, S.
虽然分子类星体吸收系统为气体的物理和化学性质提供了独特的探测器，以及对基础物理和宇宙学的原始限制，但它们的探测仍然具有挑战性。在这里，我们介绍了对39个吸收系统中分子气体的完整调查结果，这些吸收系统仅根据斯隆数字巡天(SDSS)光谱中中性碳线的检测而选择，而不需要任何原子或分子气体含量的任何先验知识。在所有12个系统中都发现了H-2(包括7个新的探测)，其中相应的线路被仪器设置覆盖，并测量到LOG N(H-2)大于或类似于18，表明是自屏蔽状态。我们还报告了7个CO检测(7/39)，降至与13.5类似的对数N(CO)，其中包括一个新的，并对其余32个系统的N(CO)施加了严格的限制。N(CO)和N(CI)与N(CO)/N(CI)有很强的相关性，接近1/10。这表明CI选择的吸收子群探测的气体比HI-H-2转变更深，在HI-H-2转变中，云中总氢气的很大一部分是以H-2的形式存在的。我们的结论是，以含碘分子为靶标是寻找高金属丰度分子吸收材料的有效途径。然而，在低金属度区域和高柱密度中性气体中的分子含量的探测仍有待进行，以揭开正常高z星系中气体转化的过程。
While molecular quasar absorption systems provide unique probes of the physical and chemical properties of the gas as well as original constraints on fundamental physics and cosmology, their detection remains challenging. Here we present the results from a complete survey for molecular gas in thirty-nine absorption systems selected solely upon the detection of neutral carbon lines in Sloan Digital Sky Survey (SDSS) spectra, without any prior knowledge of the atomic or molecular gas content. H-2 is found in all twelve systems (including seven new detections) where the corresponding lines are covered by the instrument setups and measured to have log N(H-2) greater than or similar to 18, indicating a self-shielded regime. We also report seven CO detections (7/39) down to log N(CO) similar to 13.5, including a new one, and put stringent constraints on N(CO) for the remaining 32 systems. N(CO) and N(C I) are found to be strongly correlated with N(CO)/N(C I) similar to 1/10. This suggests that the C I-selected absorber population is probing gas deeper than the H I-H-2 transition in which a substantial fraction of the total hydrogen in the cloud is in the form of H-2. We conclude that targeting C I-bearing absorbers is a very efficient way to find high-metallicity molecular absorbers. However, probing the molecular content in lower-metallicity regimes as well as high-column-density neutral gas remains to be undertaken to unravel the processes of gas conversion in normal high-z galaxies.