Red giants observed by CoRoT and APOGEE: The evolution of the Milky Way's radial metallicity gradient
Red giants observed by CoRoT and APOGEE: The evolution of the Milky Way's radial metallicity gradient
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DOI：
10.1051/0004-6361/201629363
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发表时间：
2016-08
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影响因子：
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通讯作者：
F. Anders;C. Chiappini;I. Minchev;A. Miglio;J. Montalbán;B. Mosser;T. Rodrigues;T. Rodrigues
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文献类型：
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作者：
F. Anders;C. Chiappini;I. Minchev;A. Miglio;J. Montalbán;B. Mosser;T. Rodrigues;T. Rodrigues
通过对靠近银盘面的 418 颗红巨星进行星震和光谱观测（6 kpc $<R_{\rm Gal}\lesssim13$ kpc, $|Z_{\rm Gal}|<0.3$ kpc），我们测量了银河系薄盘中径向金属丰度分布在宇宙时间内的年龄依赖性。年轻红巨星族的径向铁梯度斜率（$-0.058\pm0.008$ [stat.] $\pm0.003$ [syst.] dex/kpc）与最近的造父变星测量结果一致。对于年龄为 $1-4$ Gyr 的恒星族群，梯度稍微陡一些，值为 $-0.066\pm0.007\pm0.002$ dex/kpc，然后再次变平，对于年龄在 6 到 10 Gyr 之间的恒星，达到 $\sim-0.03$ dex/kpc 的值。我们的结果与最先进的化学动力学银河系模型非常一致，在该模型中，丰度梯度及其散射的演化可以完全用星际介质中不变的负金属丰度梯度以及恒星径向加热和迁移来解释。我们还解释了为什么太阳邻域中的中龄疏散星团的金属含量更高，以及为什么它们的径向金属丰度梯度似乎比最年轻的星团陡峭得多。在 2 Gyr 内，径向混合就可以将富含金属的簇从盘的最内部区域带到 5 至 8 kpc 的银河中心半径。我们认为这些向外迁移的星团可能不太容易受到潮汐破坏，因此使当地中龄星团金属丰度梯度变陡。我们的情景还解释了为什么在场恒星中没有看到局部铁梯度随年龄的急剧陡化。在不久的将来，来自 K2 任务的星震数据将有助于改进统计数据并更好地覆盖内盘区域，从而对银河系中心部分的演化提供更严格的约束。
Using combined asteroseismic and spectroscopic observations of 418 red-giant stars close to the Galactic disc plane (6 kpc $<R_{\rm Gal}\lesssim13$ kpc, $|Z_{\rm Gal}|<0.3$ kpc), we measure the age dependence of the radial metallicity distribution in the Milky Way's thin disc over cosmic time. The slope of the radial iron gradient of the young red-giant population ($-0.058\pm0.008$ [stat.] $\pm0.003$ [syst.] dex/kpc) is consistent with recent Cepheid measurements. For stellar populations with ages of $1-4$ Gyr the gradient is slightly steeper, at a value of $-0.066\pm0.007\pm0.002$ dex/kpc, and then flattens again to reach a value of $\sim-0.03$ dex/kpc for stars with ages between 6 and 10 Gyr. Our results are in good agreement with a state-of-the-art chemo-dynamical Milky-Way model in which the evolution of the abundance gradient and its scatter can be entirely explained by a non-varying negative metallicity gradient in the interstellar medium, together with stellar radial heating and migration. We also offer an explanation for why intermediate-age open clusters in the Solar Neighbourhood can be more metal-rich, and why their radial metallicity gradient seems to be much steeper than that of the youngest clusters. Already within 2 Gyr, radial mixing can bring metal-rich clusters from the innermost regions of the disc to Galactocentric radii of 5 to 8 kpc. We suggest that these outward-migrating clusters may be less prone to tidal disruption and therefore steepen the local intermediate-age cluster metallicity gradient. Our scenario also explains why the strong steepening of the local iron gradient with age is not seen in field stars. In the near future, asteroseismic data from the K2 mission will allow for improved statistics and a better coverage of the inner-disc regions, thereby providing tighter constraints on the evolution of the central parts of the Milky Way.