The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals
The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals
复制标题
亚阻尼莱曼α吸收体在金属宇宙演化中的作用
DOI：
10.1086/515430
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发表时间：
2006
影响因子：
4.8
通讯作者：
J. Meiring
中科院分区：
文献类型：
--
作者：
V. P. Kulkarni;P. Khare;C. Péroux;D. G. York;J. Lauroesch;J. Meiring
低平均金属丰度的阻尼莱曼α（DLA）类星体吸收体在所有的红移研究的观测似乎矛盾的全球平均星际金属丰度的星系从宇宙化学演化模型的预测。另一方面，最近已经鉴定了许多富含金属的亚DLA系统，并且富含金属的亚DLA的分数似乎显著大于富含金属的DLA的分数，特别是在z<1.5时。有鉴于此，我们在这里调查的亚DLAs的金属丰度的演变。我们发现观测到的次DLAs的平均Zn金属丰度可能高于观测到的DLAs，特别是在低红移处，在z<~ 1时达到近太阳水平。这种趋势似乎不是样本选择、锌的使用、N_{HI}加权的使用或观察灵敏度的人为因素。虽然在某些情况下，亚DLA样品中可能存在对极低金属丰度的偏倚，但这不能解释低z下DLA和亚DLA金属丰度之间的差异。DLA和亚DLA之间的差异的主要原因似乎是缺乏富含金属的DLA。我们估计分DLA的贡献，总金属预算使用的措施，其金属丰度和共动气体密度。这些计算表明，在z<~ 1时，亚DLA对总金属预算的贡献可能是DLA的几倍。在更高的红移下，也有迹象表明，亚DLAs可能对宇宙金属收支有显着贡献。
Observations of low mean metallicity of damped Lyman-alpha (DLA) quasar absorbers at all redshifts studied appear to contradict the predictions for the global mean interstellar metallicity in galaxies from cosmic chemical evolution models. On the other hand, a number of metal-rich sub-DLA systems have been identified recently, and the fraction of metal-rich sub-DLAs appears to be considerably larger than that of metal-rich DLAs, especially at z<1.5. In view of this, here we investigate the evolution of metallicity in sub-DLAs. We find that the mean Zn metallicity of the observed sub-DLAs may be higher than that of the observed DLAs, especially at low redshifts, reaching a near-solar level at z<~ 1. This trend does not appear to be an artifact of sample selection, the use of Zn, the use of N_{HI}-weighting, or observational sensitivity. While a bias against very low metallicity could be present in the sub-DLA sample in some situations, this cannot explain the difference between the DLA and sub-DLA metallicities at low z. The primary reason for the difference between the DLAs and sub-DLAs appears to be the dearth of metal-rich DLAs. We estimate the sub-DLA contribution to the total metal budget using measures of their metallicity and comoving gas density. These calculations suggest that at z<~ 1, the contribution of sub-DLAs to the total metal budget may be several times that of DLAs. At higher redshifts also, there are indications that the sub-DLAs may contribute significantly to the cosmic metal budget.