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首页> 外文期刊>The Astrophysical journal >The UCSD HIRES/Keck I Damped Lyα Abundance Database.* II. The Implications
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The UCSD HIRES/Keck I Damped Lyα Abundance Database.* II. The Implications

机译:UCSD HIRES / Keck I降低了Lyα丰度数据库。含义

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We present a comprehensive analysis of the damped Lyα (DLA) abundance database presented in the first paper of this series. This database provides a homogeneous set of abundance measurements for many elements including Si, Cr, Ni, Zn, Fe, Al, S, Co, O, and Ar from 38 DLA systems with zabs 1.5. With little exception, these DLA systems exhibit very similar relative abundances. There is no significant correlation in X/Fe with [Fe/H] metallicity, and the dispersion in X/Fe is small at all metallicity. We search the database for trends indicative of dust depletion and in a few cases find strong evidence. Specifically, we identify a correlation between [Si/Ti] and [Zn/Fe] which is unambiguous evidence for depletion. Following Hou and colleagues, we present [X/Si] abundances against [Si/H] + log N(H ) and note trends of decreasing X/Si with increasing [Si/H] + log N(H ) which argue for dust depletion. Similarly, comparisons of [Si/Fe] and [Si/Cr] against [Si/H] indicate significant depletion at [Si/H] -1 but suggest essentially dust-free damped systems at [Si/H] -1.5 dex. We present a discussion on the nucleosynthetic history of the DLA systems by focusing on abundance patterns which are minimally affected by dust depletion. We find [Si/Fe] → 0.25 dex as [Zn/Fe] → 0 and that the [Si/Fe] values exhibit a plateau of ≈0.3 dex at [Si/H] -1.5 dex. Together these trends indicate significant α-enrichment in the DLA systems at low metallicity, an interpretation further supported by the observed O/Fe, S/Fe, and Ar/Fe ratios. Comparing the relative abundances of the Fe peak elements, we identify important offsets from solar relative abundances for Cr, Ni, and Fe which suggest variations in nucleosynthesis along the Fe peak. Finally, the DLA systems exhibit a modest odd-even effect revealed by Si/Al, [Si/Al] ≈ 0.4 dex, which is significantly smaller than values observed in Galactic halo stars of comparable metallicity. These observations present strong evidence that the DLA systems and Galactic halo had different enrichment histories. To assess the impact of dust obscuration, we present estimates of the dust-to-gas ratios for the DLA sight lines and crudely calculate dust extinction corrections. The distribution of extinction corrections suggests that the effects of dust obscuration are minimal and that the population of "missing" damped systems has physical characteristics similar to the observed sample. We update our investigation on the chemical evolution of the early universe in neutral gas. The results are in good agreement with our previous work, but we emphasize two differences: (1) the unweighted and N(H I)-weighted [Fe/H] mean metallicities now have similar values at all epochs except z 3.5, where small number statistics dominate the N(H I)-weighted mean; and (2) there is no evolution in the mean [Fe/H] metallicity from z = 1.7 to 3.5 but possibly a marked drop at higher redshift. We conclude with a general discussion on the physical nature of the DLA systems. We stress the uniformity of the DLA chemical abundances which indicates that the protogalaxies identified with DLA systems have very similar enrichment histories, i.e., a nearly constant relative contribution from Type Ia and Type II supernovae. The DLA systems also show constant relative abundances within a given system, which places strict constraints on the mixing timescales of the damped systems and may pose a great challenge to the protogalactic clump scenarios favored by hierarchical galaxy formation.
机译:我们对本系列第一篇论文中介绍的阻尼Lyα(DLA)丰度数据库进行了全面分析。该数据库为zabs> 1.5的38个DLA系统中的许多元素(包括Si,Cr,Ni,Zn,Fe,Al,S,Co,O和Ar)提供了一组均匀的丰度测量值。几乎没有例外,这些DLA系统显示出非常相似的相对丰度。 X / Fe与[Fe / H]金属度之间没有显着相关性,并且X / Fe的分散度在所有金属度下均很小。我们在数据库中搜索指示粉尘枯竭的趋势,并在少数情况下找到有力的证据。具体而言,我们确定了[Si / Ti]和[Zn / Fe]之间的相关性,这是损耗的明确证据。继侯和同事之后,我们提出了[X / Si]相对于[Si / H] + log N(H)的丰度,并注意到X / Si随[Si / H] + log N(H)的增加而降低的趋势,这表明存在粉尘消耗。同样,[Si / Fe]和[Si / Cr]与[Si / H]的比较表明,[Si / H]> -1时显着耗竭,但建议[Si / H] <-1.5时基本无尘阻尼系统dex。我们通过关注受粉尘消耗影响最小的丰度模式,对DLA系统的核合成历史进行了讨论。我们发现[Si / Fe]→0.25 dex为[Zn / Fe]→0,并且[Si / Fe]值在[Si / H] <-1.5 dex时表现出约0.3 dex的平稳期。这些趋势共同表明在低金属度的情况下DLA系统中存在明显的α富集,这一解释进一步得到了观察到的O / Fe,S / Fe和Ar / Fe比的支持。比较Fe峰元素的相对丰度,我们从Cr,Ni和Fe的太阳相对丰度中发现重要的偏移量,这表明沿Fe峰的核合成存在变化。最后,DLA系统显示出适度的Si / Al奇偶效应,[Si / Al]≈0.4 dex,比在具有类似金属性的银河晕星中观察到的值小得多。这些观察结果提供了有力的证据,证明DLA系统和银河晕具有不同的富集历史。为了评估灰尘掩盖的影响,我们提出了DLA视线的灰尘与气体比率的估计值,并粗略地计算了消光校正。消光校正的分布表明,灰尘遮盖的影响最小,并且“缺失”的阻尼系统总体具有与观察到的样品相似的物理特性。我们更新了对中性气体中早期宇宙化学演化的研究。结果与我们先前的工作非常吻合,但是我们强调两个区别:(1)除z> 3.5之外,所有时期的未加权和N(HI)加权[Fe / H]均表示金属性具有相似的值。数量统计控制着N(HI)加权均值; (2)[Fe / H]的平均金属度从z = 1.7到3.5没有变化,但是在较高的红移下可能会显着下降。最后,我们对DLA系统的物理性质进行了一般性讨论。我们强调了DLA化学丰度的均匀性,这表明用DLA系统鉴定的原星系具有非常相似的富集历史,即Ia型和II型超新星的相对贡献几乎恒定。 DLA系统在给定系统内还显示出恒定的相对丰度,这对阻尼系统的混合时间尺度提出了严格的约束,并且可能对分级星系形成所青睐的原银河系团场景提出巨大挑战。

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