VIRUS-dE巡天II：矮椭圆星系中尖点且圆的暗晕——早期并合的结果？
The VIRUS-dE Survey II: Cuspy and round halos in dwarf ellipticals -- A result of early assembly?
AI总结：
该研究通过轨道建模分析矮椭圆星系暗晕的密度斜率与扁率，揭示其形态受环境、角动量和并合时期影响，支持本地dE形成于更高红移。
摘要：
我们分析了一个矮椭圆星系（dE）样本的暗物质（DM）晕，并讨论了宇宙学和演化意义。利用轨道建模，我们恢复了它们的密度斜率，并首次恢复了暗晕的扁率。我们发现“尖点—核”张力较为温和：平均而言，dE的中心斜率略低于Navarro Frenk White（NFW）预测。然而，测得的扁率仍比宇宙学模拟预测的更接近球形。与更亮的早型星系（ETG）不同，dE的总密度斜率更浅，并且其平均DM密度不遵循与光度之间的标度关系。相反，dE暗晕比晚型星系（LTG）中的暗晕更致密，密度斜率也更陡。我们发现平均DM密度和斜率与环境强相关，并与角动量中等相关。位于中心、不旋转的dE具有致密且呈尖点状的暗晕，而室女座外围旋转的dE则更具核状结构且密度较低。这可以由星系团外围dE形成较晚来解释，或者也可以由外围dE在其截然不同的恒星形成历史中所经历的累积重子反馈来解释。我们的结果表明，暗晕轮廓并非普遍适用（它们取决于并合条件），并且由于内部反馈，它们只发生温和演化。我们得出结论：本地宇宙中的dE比本地螺旋星系在更高的红移处完成并合。在这些极端条件下（例如恒星形成、暗晕并合）情况曾非常不同，这表明当前没有新的dE形成。
英文摘要：
We analyze the dark matter (DM) halos of a sample of dwarf Ellitpicals (dE) and discuss cosmological and evolutionary implications. Using orbit modeling we recover their density slopes and, for the first time, the halo flattening. We find the `cusp-core' tension is mild, on average dEs have central slopes slightly below the Navarro Frenk White (NFW) predictions. However, the measured flattenings are still more spherical than cosmological simulations predict. Unlike brighter ETGs the total density slopes of dEs are shallower, and their average DM density does not follow their scaling relation with luminosity. Conversely, dE halos are denser and the densities steeper than in LTGs. We find average DM density and slope are strongly correlated with the environment and moderately with the angular momentum. Central, non-rotating dEs have dense and cuspy halos, whereas rotating dEs in Virgo's outskirts are more cored and less dense. This can be explained by a delayed formation of the dEs in the cluster outskirts, or alternatively, by the accumulated baryonic feedback the dEs in the outskirts have experienced during their very different star formation history. Our results suggest halo profiles are not universal (they depend on assembly conditions) and they evolve only mildly due to internal feedback. We conclude dEs in the local Universe have assembled at a higher redshift than local spirals. In these extreme conditions (e.g. star-formation, halo assembly) were very different, suggesting no new dEs are formed at present.
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