THE ORIGIN AND EVOLUTION OF METALLICITY GRADIENTS: PROBING THE MODE OF MASS ASSEMBLY AT z ≃ 2
THE ORIGIN AND EVOLUTION OF METALLICITY GRADIENTS: PROBING THE MODE OF MASS ASSEMBLY AT z ≃ 2
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DOI：
10.1088/0004-637x/765/1/48
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发表时间：
2012-07
期刊：
影响因子：
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通讯作者：
T. Jones;R. Ellis;J. Richard;E. Jullo
中科院分区：
文献类型：
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作者：
T. Jones;R. Ellis;J. Richard;E. Jullo
我们提出和讨论的气相金属丰度梯度的测量在四个引力透镜星系z = 2.0-2.4的基础上自适应光学辅助成像光谱与凯克II望远镜。三个星系有序旋转揭示金属丰度梯度较低的气相金属丰度在较大的银河系中心半径。其中两个显示的梯度比本地发现的要陡得多，而第三个显示的梯度与本地盘状星系相似。第四个星系表现出复杂的运动学，表明正在进行的合并，并揭示了一个“倒置”的梯度与较低的金属丰度在中心地区。通过将我们的样本与文献中关于低红移星系的类似数据进行比较，我们确定，平均而言，金属丰度梯度在z = 2.2和当前历元之间必须平坦2.6 ± 0.9倍。这个因素与大质量星系的尺寸增长大致一致，这表明由内而外的增长可以解释金属丰度梯度的演变。由于我们新数据的添加首次表明了这种进化的连贯性，因此我们开发了一个简单的化学进化模型来解释集体数据。我们发现，金属丰度梯度和它们的演变可以解释由向内的径向迁移的气体一起的径向变化的质量负载因子控制流出的气体的比例，当地的星星形成率。从我们的模型中推导出的平均质量负载因子与z <$2星系外流气体的直接测量结果吻合得很好。
We present and discuss measurements of the gas-phase metallicity gradient in four gravitationally lensed galaxies at z = 2.0–2.4 based on adaptive optics-assisted imaging spectroscopy with the Keck II telescope. Three galaxies with well-ordered rotation reveal metallicity gradients with lower gas-phase metallicities at larger galactocentric radii. Two of these display gradients much steeper than found locally, while a third has one similar to that seen in local disk galaxies. The fourth galaxy exhibits complex kinematics indicative of an ongoing merger and reveals an “inverted” gradient with lower metallicity in the central regions. By comparing our sample to similar data in the literature for lower redshift galaxies, we determine that, on average, metallicity gradients must flatten by a factor of 2.6 ± 0.9 between z = 2.2 and the present epoch. This factor is in rough agreement with the size growth of massive galaxies, suggesting that inside-out growth can account for the evolution of metallicity gradients. Since the addition of our new data provides the first indication of a coherent picture of this evolution, we develop a simple model of chemical evolution to explain the collective data. We find that metallicity gradients and their evolution can be explained by the inward radial migration of gas together with a radial variation in the mass loading factor governing the ratio of outflowing gas to the local star formation rate. Average mass loading factors of ≲ 2 are inferred from our model in good agreement with direct measurements of outflowing gas in z ≃ 2 galaxies.