The Relationship between Age, Metallicity, and Abundances for Disk Stars in a Simulated Milky Way
The Relationship between Age, Metallicity, and Abundances for Disk Stars in a Simulated Milky Way
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DOI：
10.3847/1538-4357/aca1c7
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发表时间：
2022-04
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影响因子：
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通讯作者：
A. Carrillo;M. Ness;K. Hawkins;R. Sanderson;Kaile Wang;A. Wetzel;Matthew A. Bellardini
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作者：
A. Carrillo;M. Ness;K. Hawkins;R. Sanderson;Kaile Wang;A. Wetzel;Matthew A. Bellardini
对银河系低α圆盘的观测表明，在固定的金属丰度下，几种元素丰度与年龄相关，在年龄-[X/Fe]关系附近有独特的斜率和较小的散布。在这项研究中，我们转向模拟来探索C，N，O，Mg，Si，S和Ca元素的年龄-[X/Fe]关系，这些元素在FIRE-2宇宙放大模拟中被追踪，并理解是什么物理条件引起了观察到的年龄-[X/Fe]趋势。我们首先探索了单龄人口在其出生和当前位置[Fe/H]和[X/Fe]的分布，并找到了年龄为<；7 Gyr的恒星由内向外径向生长的证据。然后我们研究了M12I盘中年龄与[X/Fe]的关系，发现除了C、O和Ca外，趋势的方向与观测一致，内禀散射非常小，σINT(0.01Dex 0.04Dex)。在模拟中测得的σINT也是金属丰度相关的，σINT≈0.025 Dex在[Fe/H]=−0.25Dex，而σInt≈0.015 Dex在[Fe/H]=0Dex，在GALAH调查中也看到了类似的金属丰度依赖关系。此外，我们发现σINT在内星系中更高，那里的恒星年龄较大，在化学均质较差的环境中形成。年龄-[X/Fe]关系及其周围的小散射表明，模拟捕捉到了与银河系中观察到的类似的化学富集度差异，这是由于恒星在给定的出生地点和时间具有类似的元素丰度。
Observations of the Milky Way’s low-α disk show that several element abundances correlate with age at fixed metallicity, with unique slopes and small scatters around the age–[X/Fe] relations. In this study, we turn to simulations to explore the age–[X/Fe] relations for the elements C, N, O, Mg, Si, S, and Ca that are traced in a FIRE-2 cosmological zoom-in simulation of a Milky Way–like galaxy, m12i, and understand what physical conditions give rise to the observed age–[X/Fe] trends. We first explore the distributions of mono-age populations in their birth and current locations, [Fe/H], and [X/Fe], and find evidence for inside-out radial growth for stars with ages <7 Gyr. We then examine the age–[X/Fe] relations across m12i’s disk and find that the direction of the trends agrees with observations, apart from C, O, and Ca, with remarkably small intrinsic scatters, σ int (0.01 − 0.04 dex). This σ int measured in the simulations is also metallicity dependent, with σ int ≈ 0.025 dex at [Fe/H] = −0.25 dex versus σ int ≈ 0.015 dex at [Fe/H] = 0 dex, and a similar metallicity dependence is seen in the GALAH survey for the elements in common. Additionally, we find that σ int is higher in the inner galaxy, where stars are older and formed in less chemically homogeneous environments. The age–[X/Fe] relations and the small scatter around them indicate that simulations capture similar chemical enrichment variance as observed in the Milky Way, arising from stars sharing similar element abundances at a given birth place and time.