AI 中文总结
本文研究低密度环境中两个宁静低表面亮度矮星系，利用KCWI光谱分析其恒星族群，发现其梯度特征特殊，结合球状星团性质探讨熄灭机制，指出单一机制无法解释观测结果。
AI 中文摘要
位于低密度环境、拥有宁静恒星族群的矮星系极为罕见，其恒星熄灭机制高度不确定。本文介绍两个低表面亮度矮星系，它们具有大于1.2千秒差距的大有效半径，此前在Dragonfly超宽巡天中被发现，我们利用凯克II望远镜上的KCWI仪器获取了它们的光谱。我们在延伸至1.25倍有效半径的多个径向区间推导了它们的恒星族群和恒星形成历史。整体而言，两个星系均年老（约9亿年）且贫金属（[M/H]约-1），呈现出相对快速（约10亿年）的熄灭过程。我们发现两个星系的年龄和金属丰度梯度呈平坦至上升趋势，这与超弥散星系的观测结果相似，但与典型经典矮星系及模拟预测形成对比。其中一个星系DFUWS 68拥有多个球状星团，我们发现这些星团与宿主星系具有相似的年龄、金属丰度和熄灭时标。我们简要讨论了可能的熄灭机制，认为宇宙网剥离或内部反馈过程单独均无法解释我们的观测结果。
英文摘要
Dwarf galaxies located in low density environments that have quiescent stellar populations are extremely rare and the mechanism for quenching their stars is highly uncertain. Here we present two low surface brightness dwarf galaxies with large (>1.2 kpc) effective radii that were previously identified in the Dragonfly Ultrawide Survey for which we have obtained spectra using the KCWI instrument on the Keck II telescope. We derive their stellar populations and star formation histories in several radial bins out to 1.25 effective radii. Globally both galaxies are old (~9 Gyr) and metal-poor ([M/H] ~ -1) and reveal quenching on a relatively rapid timescale (~1 Gyr). We find flat to rising age and metallicity gradients in both galaxies. This is similar to those seen in ultra diffuse galaxies but is in contrast with typical classical dwarf galaxies and predictions from simulations. One galaxy, DFUWS 68, hosts several globular clusters which we find to share similar ages, metallicities and quenching timescales to that of the host galaxy stars.We briefly discuss possible quenching mechanisms and suggest that neither cosmic web stripping nor internal feedback processes alone can explain our results.
Comments12 pages, accepted for publication in MNRAS
