We explore the origin of stellar metallicity gradients in simulated and observed dwarf galaxies. We use FIRE-2 cosmological baryonic zoom-in simulations of 26 isolated galaxies as well as existing observational data for 10 Local Group dwarf galaxies. Our simulated galaxies have stellar masses between $10^{5.5}$ and $10^{8.6} \msun$. We find that stellar metallicity gradients are common in our simulations, with central regions tending to be more metal-rich than the outer parts. The strength of the gradient is correlated with galaxy-wide median stellar age, such that galaxies with younger stellar populations have flatter gradients. The strengths of these gradients are set by two competing processes: (1) the steady "puffing" of old, metal-poor stars by feedback-driven potential fluctuations, and (2) extended, late-time star formation. Late-time star formation tends to be metal rich, so galaxies with significant late-time star formation will mitigate the gradients formed by the "puffing" process. We use published results from ten Local Group dwarf galaxies to show that our predicted relationship between age and stellar metallicity-gradient strength is consistent with existing observations. This suggests that observed stellar metallicity gradients may be driven largely by the baryon/feedback cycle rather than by external environmental effects.

中文翻译：

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矮星系中恒星金属度梯度与星系年龄的关系

我们探索了模拟和观测到的矮星系中恒星金属丰度梯度的起源。我们使用 26 个孤立星系的 FIRE-2 宇宙学重子放大模拟以及 10 个本地群矮星系的现有观测数据。我们模拟的星系的恒星质量介于 $10^{5.5}$ 和 $10^{8.6}\msun$ 之间。我们发现恒星金属丰度梯度在我们的模拟中很常见，中心区域往往比外部更富含金属。梯度的强度与整个星系的中位恒星年龄相关，因此具有较年轻恒星群的星系具有更平坦的梯度。这些梯度的强度由两个相互竞争的过程决定：（1）通过反馈驱动的潜在波动稳定“膨胀”旧的、贫金属的恒星，以及（2）延长的晚期恒星形成。晚期恒星形成往往富含金属，因此具有显着晚期恒星形成的星系将减轻由“膨胀”过程形成的梯度。我们使用来自十个本地群矮星系的已发表结果来表明我们预测的年龄与恒星金属丰度梯度强度之间的关系与现有观测结果一致。这表明观测到的恒星金属丰度梯度可能主要由重子/反馈循环驱动，而不是由外部环境影响驱动。我们使用来自十个本地群矮星系的已发表结果来表明我们预测的年龄与恒星金属丰度梯度强度之间的关系与现有观测结果一致。这表明观测到的恒星金属丰度梯度可能主要由重子/反馈循环驱动，而不是由外部环境影响驱动。我们使用来自十个本地群矮星系的已发表结果来表明我们预测的年龄与恒星金属丰度梯度强度之间的关系与现有观测结果一致。这表明观测到的恒星金属丰度梯度可能主要由重子/反馈循环驱动，而不是由外部环境影响驱动。