ON THE CHEMICAL AND STRUCTURAL EVOLUTION OF THE GALACTIC DISK
ON THE CHEMICAL AND STRUCTURAL EVOLUTION OF THE GALACTIC DISK
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DOI：
10.1088/0004-637x/788/1/89
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发表时间：
2014-05
期刊：
影响因子：
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通讯作者：
Daisuke Toyouchi;M. Chiba
中科院分区：
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作者：
Daisuke Toyouchi;M. Chiba
我们研究了银河系恒星盘中径向金属丰度梯度的详细性质，以约束其化学和结构演化。为此，我们选择并分析了来自斯隆数字巡天（SDSS）和高精度径向速度行星搜索（HARPS）两个数据集的约18,500颗盘状恒星。在这些观测中，我们研究了沿恒星引导中心半径Rg的金属丰度梯度Δ[Fe/H]/ΔRg及其对[α/Fe]比值的依赖，从而推断出这些恒星形成的气体盘的原始金属丰度分布及其时间演化。在两个样本源中，高[α/Fe]比值（SDSS中[α/Fe] > 0.3， HARPS中[α/Fe] > 0.2）的厚盘候选恒星显示出正的Δ[Fe/H]/ΔRg，而低[α/Fe]比值的薄盘候选恒星显示出负的Δ[Fe/H]/ΔRg。此外，我们发现相对年轻的薄盘种群具有低得多的[α/Fe]比率（SDSS中[α/Fe] < 0.2， HARPS中[α/Fe] < 0.1），与具有较高[α/Fe]比率（SDSS中[α/Fe] ~ 0.2， HARPS中[α/Fe] ~ 0.1）的老年种群相比，随着[α/Fe]比率的降低，明显呈现出平坦的Δ[Fe/H]/ΔRg。在星系形成过程中，原始气体迅速涌入盘内区域，产生正的金属丰度梯度，随后盘的化学演化导致金属丰度梯度在后期的平坦化效应，讨论了早期盘演化的可能含义。
We study the detailed properties of the radial metallicity gradient in the stellar disk of our Galaxy to constrain its chemical and structural evolution. For this purpose we select and analyze ∼18,500 disk stars taken from two data sets, the Sloan Digital Sky Survey (SDSS) and the High-Accuracy Radial velocity Planetary Searcher (HARPS). On these surveys we examine the metallicity gradient, Δ[Fe/H]/ΔRg, along the guiding center radii, Rg, of stars and its dependence on the [α/Fe] ratios to infer the original metallicity distribution of the gas disk from which those stars formed and its time evolution. In both sample sources, the thick-disk candidate stars characterized by high [α/Fe] ratios ([α/Fe] > 0.3 in SDSS, [α/Fe] > 0.2 in HARPS) are found to show a positive Δ[Fe/H]/ΔRg, whereas the thin-disk candidate stars characterized by lower [α/Fe] ratios show a negative one. Furthermore, we find that the relatively young thin-disk population characterized by much lower [α/Fe] ratios ([α/Fe] < 0.2 in SDSS, [α/Fe] < 0.1 in HARPS) notably shows a flattening Δ[Fe/H]/ΔRg with decreasing [α/Fe], in contrast to the old one with higher [α/Fe] ratios ([α/Fe] ∼ 0.2 in SDSS, [α/Fe] ∼ 0.1 in HARPS). The possible implication for early disk evolution is discussed in the context of galaxy formation accompanying the rapid infall of primordial gas on the inner disk region, which can generate a positive metallicity gradient, and the subsequent chemical evolution of the disk, which results in a flattening effect of a metallicity gradient at later epochs.