42个本地体积矮星系的径向恒星年龄梯度
Radial Stellar Age Gradients in 42 Local Volume Dwarf Galaxies
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中文总结 AI 辅助
本研究测量42个本地体积矮星系的径向恒星年龄梯度，发现τ90梯度与全局恒星形成历史显著相关，可用于区分不同恒星反馈机制的模拟，支持矮星系从内向外形成的预测。
中文摘要 AI 辅助
我们对42个本地体积矮星系（恒星质量的对数范围为6≤Log M★/M⊙≤9）的恒星形成历史（SFHs）进行拟合，这些星系的 resolved 色-星等图（CMDs）被空间划分为椭圆环带，由此测量得到径向恒星年龄梯度。每个环带内的年龄用τ90和τ50量化，τ90和τ50分别对应形成90%和50%累积恒星质量的回溯时间。我们发现，径向年龄梯度与环境无相关性，但τ90梯度与星系终身的“全局”恒星形成历史（SFHs）显著相关（p值≤0.001），这与两个独立的宇宙学zoom-in模拟结果一致；而对于τ50的径向梯度，模拟预测存在差异。我们证明，鉴于我们的观测样本规模大（N=42）且多样性高，观测到的与全局SFH的相关强度是一个可用于区分具有不同恒星反馈机制的不同模拟的可行参数。总体而言，我们的结果支持矮星系像质量更大的星系一样从内向外形成的预测，由反馈驱动的恒星向外径向迁移，以及年轻恒星群体的出生半径增大，共同导致了从外向内到平坦的当前恒星年龄梯度。此外，τ50梯度与全局SFH缺乏相关性，这反对了径向外流气体中存在近期恒星形成的观点。我们还讨论了观测样本与最新模拟中可用样本之间差异的影响，强调了未来研究的方向。
英文摘要
We present radial stellar age gradients measured from star formation histories (SFHs) fit to resolved color-magnitude diagrams (CMDs) of 42 Local Volume dwarfs (6$\lesssim$Log M$_{\star}$/M$_{\odot}$$\lesssim$9), spatially divided into elliptical annuli. Ages in each annulus are quantified using $τ_{90}$ and $τ_{50}$, the lookback times to form 90% and 50% of the cumulative stellar mass. We find that radial age gradients are uncorrelated with environment, but gradients in $τ_{90}$ are significantly correlated ($p$-values$\lesssim$0.001) with lifetime galaxy-wide "global" SFHs, in agreement with two independent cosmological zoom-in simulations. For radial gradients of $τ_{50}$, simulation predictions differ. We demonstrate that given our large (N=42) and diverse observational sample, the strength of an observed correlation with global SFH is an actionable parameter to discriminate between different simulations with differing stellar feedback prescriptions. Overall, our results support predictions that dwarfs form inside-out like their more massive counterparts, with a combination of feedback-driven outward radial stellar migration and increasing birth radii for young stellar populations yielding present-day stellar age gradients ranging from outside-in to flat. In addition, the lack of a correlation between $τ_{50}$ gradients and global SFH argues against recent star formation in radially outflowing gas. We also discuss the impact of differences between our observational sample and samples available in the latest simulations, highlighting areas for future investigation.
