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arXiv 1905.08309astro-ph.GA
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他在盘状星系中大量存在-- I。宇宙化学动力学模拟的预测

He abundances in disc galaxies -- I. Predictions from cosmological chemodynamical simulations

Fiorenzo Vincenzo, Andrea Miglio, Chiaki Kobayashi, J. Ted Mackereth, Josefina Montalban

备注：
Accepted for publication in A&A
发表信息：
A&A 630, A125 (2019)
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摘要：

我们研究如何恒星和气相的He丰度演化为模拟的恒星形成盘星系内不同的恒星形成历史的时间函数。我们利用宇宙化学动力学模拟的星系形成和演化，其中包括恒星的形成，以及能量和化学富集的反馈，从渐近巨星分支星，核心坍缩超新星，Ia型超新星。在我们模拟的盘星系的星际介质中，He质量分数$Y$和金属丰度$Z$之间的预测关系依赖于过去的星系恒星形成历史。特别是，$dY/dZ$不是恒定的，而是随着时间的变化而变化，这取决于我们选择追踪$Z$的特定化学元素;特别是，$dY/dX_{\text{O}}$和$dY/dX_{\text{C}}$随着时间的变化而增加，而$dY/dX_{\text{N}}$则减少。在气相中，我们发现负径向梯度的$Y$，由于我们模拟的星系盘的内向外增长作为时间的函数，这引起了较长的化学富集的时间尺度外星系区域，在那里我们发现较低的平均值为$Y$和$Z$。最后，通过化学演化模型，在银河系的隆起和内部盘，我们预测陡峭的$Y$与年龄的关系，在高$Z$比在星系外区域。我们的结论是，对于恒星模型中假设的$Y$ - $Z$关系的校准，C，N和C+N是比O更好的金属丰度代理，因为它们显示更陡峭和更少的分散关系。

英文摘要：

We investigate how the stellar and gas-phase He abundances evolve as functions of time within simulated star-forming disc galaxies with different star formation histories. We make use of a cosmological chemodynamical simulation for galaxy formation and evolution, which includes star formation, as well as energy and chemical enrichment feedback from asymptotic giant branch stars, core-collapse supernovae, and Type Ia supernovae. The predicted relations between the He mass fraction, $Y$, and the metallicity, $Z$, in the interstellar medium of our simulated disc galaxies depend on the past galaxy star formation history. In particular, $dY/dZ$ is not constant and evolves as a function of time, depending on the specific chemical element that we choose to trace $Z$; in particular, $dY/dX_{\text{O}}$ and $dY/dX_{\text{C}}$ increase as functions of time, whereas $dY/dX_{\text{N}}$ decreases. In the gas-phase, we find negative radial gradients of $Y$, due to the inside-out growth of our simulated galaxy discs as a function of time; this gives rise to longer chemical enrichment time scales in the outer galaxy regions, where we find lower average values for $Y$ and $Z$. Finally, by means of chemical evolution models, in the galactic bulge and inner disc, we predict steeper $Y$ versus age relations at high $Z$ than in the outer galaxy regions. We conclude that, for calibrating the assumed $Y$-$Z$ relation in stellar models, C, N, and C+N are better proxies for the metallicity than O, because they show steeper and less scattered relations.

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