We use FIRE-2 simulations to examine 3D variations of gas-phase elemental abundances of [O/H], [Fe/H], and [N/H] in 11 MW and M31-mass galaxies across their formation histories at z ≤ 1.5 ($t_{\rm lookback} \le 9.4 \, \rm {Gyr}$), motivated by characterizing the initial conditions of stars for chemical tagging. Gas within $1 \, \rm {kpc}$ of the disc mid-plane is vertically homogeneous to $\lesssim 0.008 \, \rm {dex}$ at all z ≤ 1.5. We find negative radial gradients (metallicity decreases with galactocentric radius) at all times, which steepen over time from $\approx \! -0.01 \, \rm {dex}\, \rm {kpc}^{-1}$ at z = 1 ($t_{\rm lookback} = 7.8 \, \rm {Gyr}$) to $\approx \! -0.03 \, \rm {dex}\, \rm {kpc}^{-1}$ at z = 0, and which broadly agree with observations of the MW, M31, and nearby MW/M31-mass galaxies. Azimuthal variations at fixed radius are typically $0.14 \, \rm {dex}$ at z = 1, reducing to $0.05 \, \rm {dex}$ at z = 0. Thus, over time radial gradients become steeper while azimuthal variations become weaker (more homogeneous). As a result, azimuthal variations were larger than radial variations at z ≳ 0.8 ($t_{\rm lookback} \gtrsim 6.9 \, \rm {Gyr}$). Furthermore, elemental abundances are measurably homogeneous (to ≲0.05 dex) across a radial range of $\Delta R \approx 3.5 \, \rm {kpc}$ at z ≳ 1 and $\Delta R \approx 1.7 \, \rm {kpc}$ at z = 0. We also measure full distributions of elemental abundances, finding typically negatively skewed normal distributions at z ≳ 1 that evolve to typically Gaussian distributions by z = 0. Our results on gas abundances inform the initial conditions for stars, including the spatial and temporal scales for applying chemical tagging to understand stellar birth in the MW.

中文翻译：

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FIRE 模拟中银河系质量星系形成历史的 3D 气相元素丰度：化学标记的初始条件

我们使用 FIRE-2 模拟来检查 11 MW 和 M31 质量星系在 z ≤ 的形成历史中的气相元素丰度的 3D 变化1.5 ($t_{\rm 回溯} \le 9.4 \, \rm {Gyr}$)，其动机是表征恒星的初始条件以进行化学标记。圆盘中平面 $1 \, \rm {kpc}$ 内的气体在 z ≤ 1.5 处与 $\lesssim 0.008 \, \rm {dex}$ 垂直均匀。我们始终发现负径向梯度（金属度随半心半径降低），随着时间的推移从 $\approx \! -0.01 \, \rm {dex}\, \rm {kpc}^{-1}$ at z = 1 ($t_{\rm lookback} = 7.8 \, \rm {Gyr}$) 到 $\approx \ ！-0.03 \, \rm {dex}\, \rm {kpc}^{-1}$ 在 z = 0 时，与对 MW、M31 和附近 MW/M31 质量星系的观测大体一致。固定半径处的方位角变化通常为 $0.14 \, \rm {dex}$ 在 z = 1 处，减少到 $0.05 \, \rm {dex}$ 在 z = 0 处。因此，随着时间的推移，径向梯度变得更陡峭，而方位角变化变得更弱（更均匀）。因此，在 z ≳ 0.8 ($t_{\rm lookback} \gtrsim 6.9 \, \rm {Gyr}$) 时，方位角变化大于径向变化。此外，元素丰度在 $\Delta R \约 3.5 \, \rm {kpc}$ at z ≳ 1 和 $\Delta R \约 1.7 \, \rm { kpc}$ 在 z = 0 时。我们还测量了元素丰度的完整分布，在 z ≳ 1 处发现典型的负偏正态分布，在 z = 0 时演变为典型的高斯分布。我们关于气体丰度的结果为恒星的初始条件提供了信息，