标题： 金属丰度在z < 1.5：对大 Lyman alpha 系统化学富集历史的新线索 显示英文标题

标题： Metal Abundances at z < 1.5: Fresh Clues to the Chemical Enrichment History of Damped Lyman alpha Systems

摘要： 我们探索了红移演化的强Lyman alpha系统（DLAs）的金属含量，对z < 1.5的四个吸收体进行了新的观测。主要结论是，柱密度加权平均金属度[<Zn/H>] = -1.03 +/- 0.23（在对数尺度上），在z < 1.5时并不比早期时期显著更高，尽管此时宇宙的共动恒星形成率密度接近其最大值。对于四个DLAs中的三个，我们的观测包括Si、Mn、Cr、Fe和Ni的吸收线，以及Zn。我们认为这些元素的相对丰度与中等程度的尘埃消耗一致，一旦考虑进去，就不会为银河系中金属贫乏恒星中看到的α-元素相对于铁的增强留下空间。这与之前的断言相反，即DLAs仅由II型超新星富集，但如果所研究系统的恒星形成速率比我们银河系早期历史中的恒星形成速率更缓慢，则可以理解这一点。这些结果增加了越来越多的数据，所有数据都指向一个结论，即已知的DLAs并不能追踪负责大部分恒星形成的星系群体。可能的原因是通过金属丰富的气体视线系统性地被低估，因为背景类星体被变红，而且最活跃的恒星形成星系也是最紧凑的，其横截面太小，目前样本的有限统计数据尚未探测到。 显示英文摘要

摘要： We explore the redshift evolution of the metal content of damped Lyman alpha systems (DLAs) with new observations of four absorbers at z < 1.5 . The main conclusion is that the column density--weighted mean metallicity, [<Zn/H>] = -1.03 +/- 0.23 (on a logarithmic scale), is not significantly higher at z < 1.5 than at earlier epochs, despite the fact that the comoving star formation rate density of the universe was near its maximum value at this redshift. For three of the four DLAs our observations include absorption lines of Si, Mn, Cr, Fe, and Ni, as well as Zn. We argue that the relative abundances of these elements are consistent with a moderate degree of dust depletion which, once accounted for, leaves no room for the enhancement of the alpha-elements over iron seen in metal poor stars in the Milky Way. This is contrary to previous assertions that DLAs have been enriched solely by Type II supernovae, but can be understood if the rate of star formation in the systems studied proceeded more slowly than in the early history of our Galaxy. These results add to a growing body of data all pointing to the conclusion that known DLAs do not trace the galaxy population responsible for the bulk of star formation. Possible reasons are that sight-lines through metal rich gas are systematically underrepresented because the background QSOs are reddened, and that the most actively star forming galaxies are also the most compact, presenting too small a cross-section to have been probed yet with the limited statistics of current samples.