The Earliest Phases of Galaxy Evolution
The Earliest Phases of Galaxy Evolution
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星系演化的最早阶段
DOI：
10.1086/307006
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
K. Nomoto
中科院分区：
文献类型：
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作者：
C. Chiappini;F. Matteucci;T. Beers;K. Nomoto
在本文中，我们研究的非常早期阶段的演变，我们的银河系的化学演化模型，再现了大部分的观测约束，在太阳附近和磁盘。我们将分析限制在太阳附近，并且我们提出了几种元素（C，N，O，Mg，Si，S，Ca和Fe）的预测丰度，其金属丰度范围比以前的模型更广，[Fe/H]=-4.0到[Fe/H]=0.0。我们采用最新的产量计算的大质量恒星从两个不同的作品，并比较结果与一个非常大的样本的数据，有史以来最大的用于此目的。我们已经获得了这一数据集，通过选择最新的和更高质量的丰度数据，从一些来源，并重新归一化到相同的太阳丰度。这些数据已经用一种新的强大的统计方法进行了分析，使我们能够量化测量元素丰度的观测分布，并与我们的化学演化模型的预测进行更有意义的比较。我们的分析表明，在低金属丰度（-3.0<[Fe/H]<-1.0）下，[α/Fe]比的“平台”不是完全恒定的，而是一个斜率，特别是对于氧。我们的模型在两组产量下都很好地再现了这个斜率。这并不奇怪，因为现实的化学演化模型，考虑到恒星寿命的细节，从来没有预测过一个完全平坦的平台。这要么是由于不同质量的大质量恒星产生略有不同的O/Fe比，要么是由于经常被遗忘的事实，即起源于白色矮星的Ia型超新星已经在银河年龄30万年时开始出现，并在1 Gyr时达到最大值。对于较低的金属丰度（-4.0<[Fe/H]<-3.0），两组采用的产率不同，特别是对于铁。在这个范围内，“平台”几乎是恒定的，因为在如此低的金属丰度下，几乎没有Ia型超新星的贡献。然而，在这个领域没有足够的数据来检验这一点。最后，我们显示的演化与红移的[O/Fe]比为不同的宇宙学，并得出结论，这一比例的急剧上升，应观察到在高红移，无论采用的产量。[O/Zn]比值也会有同样的行为，因为这些元素不太可能受到尘埃的影响，所以应该更容易与高红移阻尼Lyα系统中观测到的丰度进行比较。未来对贫金属恒星[α/Fe]或[α/Zn]比值的测量将有助于推断高红移天体的性质和年龄。
In this paper we study the very early phases of the evolution of our Galaxy by means of a chemical evolution model that reproduces most of the observational constraints in the solar vicinity and in the disk. We have restricted our analysis to the solar neighborhood, and we present the predicted abundances of several elements (C, N, O, Mg, Si, S, Ca, and Fe) over a more extended range of metallicities, [Fe/H]=-4.0 to [Fe/H]=0.0, than previous models. We adopt the most recent yield calculations for massive stars taken from two different works, and compare the results with a very large sample of data, one of the largest ever used for this purpose. We have obtained this data set by selecting the most recent and higher quality abundance data from a number of sources and renormalizing them to the same solar abundances. These data have been analyzed with a new and powerful statistical method that allows us to quantify the observational spread in measured elemental abundances and to obtain a more meaningful comparison with the predictions from our chemical evolution model. Our analysis shows that the "plateau" observed for the [α/Fe] ratios at low metallicities (-3.0<[Fe/H]<-1.0) is not perfectly constant, but shows a slope, especially for oxygen. This slope is very well reproduced by our model with both sets of yields. This is not surprising, since realistic chemical evolution models, taking stellar lifetimes into account in detail, never predicted a completely flat plateau. This is due either to the fact that massive stars of different mass produce a slightly different O/Fe ratio or to the often forgotten fact that supernovae of type Ia, originating from white dwarfs, already start appearing at a Galactic age of 30 Myr and reach their maximum at 1 Gyr. For lower metallicities (-4.0<[Fe/H]<-3.0), the two sets of adopted yields differ, especially for iron. In this range, the "plateau" is almost constant, since at such low metallicities there is almost no contribution from type Ia supernovae. However, there are not enough data in this domain to significantly test this point. Finally, we show the evolution with redshift of the [O/Fe] ratio for different cosmologies and conclude that a sharp rise of this ratio should be observed at high redshift, irrespective of the adopted yields. The same behavior is expected for the [O/Zn] ratio, which should be easier to compare with the abundances observed in high-redshift damped Lyα systems, since these elements are not likely to be affected by dust. Future measurements of either [α/Fe] or [α/Zn] ratios in very metal poor stars will be useful to infer the nature and the age of high-redshift objects.
九州大学
DOI：
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