The Mass-Metallicity Relation at z≳2
The Mass-Metallicity Relation at z≳2
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DOI：
10.1086/503623
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发表时间：
2006-02
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影响因子：
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通讯作者：
D. Erb;A. Shapley;M. Pettini;C. Steidel;N. Reddy;K. Adelberger
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作者：
D. Erb;A. Shapley;M. Pettini;C. Steidel;N. Reddy;K. Adelberger
我们利用87个静止坐标系中平均光谱红移为2.26 ± 0.17的紫外选择成星星系样本，研究了高红移下金属丰度与恒星质量的相关性。利用SED拟合得到的恒星质量与0.3-8 μm测光观测值，将样品按恒星质量分为6个仓，并由每个仓中的所有天体构造6个合成Hα ~+ [N ]谱。我们从[N II]/Hα比值估计了每个仓中的平均氧丰度，发现金属丰度随着恒星质量的增加而单调增加，从12 + log（O/H）< 8.2（对于M = 2.7 × 109 M的星系）到12 + log（O/H）= 8.6（对于M = 1.0 × 1011 M的星系）。我们使用SFR密度和气体密度之间的经验关系来估计星系的气体分数，发现气体分数随着恒星质量的减小而增加。这些气体的分数，结合所观察到的金属丰度，允许估计的有效产量yeff作为恒星质量的函数，在bastast到本地宇宙的观测，这表明yeff随着重子质量的减少而减少，我们发现略有增加。这种金属丰度随气体分数的变化最好用一个具有超太阳产额和流出速率比SFR高4倍的模型来拟合。我们的结论是，在高红移的质量-金属丰度的关系是由金属丰度的增加驱动的气体部分减少通过星星形成，并可能调制的金属损失从强流出星系的所有质量。
We use a sample of 87 rest-frame UV-selected star-forming galaxies with mean spectroscopic redshift ⟨z⟩ = 2.26 ± 0.17 to study the correlation between metallicity and stellar mass at high redshift. Using stellar masses determined from SED fitting to observed 0.3-8 μm photometry, we divide the sample into six bins in stellar mass and construct six composite Hα + [N ] spectra from all of the objects in each bin. We estimate the mean oxygen abundance in each bin from the [N II]/Hα ratio and find a monotonic increase in metallicity with increasing stellar mass, from 12 + log(O/H) < 8.2 for galaxies with ⟨M⋆⟩ = 2.7 × 109 M☉ to 12 + log(O/H) = 8.6 for galaxies with ⟨M⋆⟩ = 1.0 × 1011 M☉. We use the empirical relation between SFR density and gas density to estimate the gas fractions of the galaxies, finding an increase in gas fraction with decreasing stellar mass. These gas fractions, combined with the observed metallicities, allow the estimation of the effective yield yeff as a function of stellar mass; in constrast to observations in the local universe, which show a decrease in yeff with decreasing baryonic mass, we find a slight increase. Such a variation of metallicity with gas fraction is best fitted by a model with supersolar yield and an outflow rate ~4 times higher than the SFR. We conclude that the mass-metallicity relation at high redshift is driven by the increase in metallicity as the gas fraction decreases through star formation and is likely modulated by metal loss from strong outflows in galaxies of all masses.