标题： 星系引起的暗物质晕转换 显示英文标题

标题： Galaxy-Induced Transformation of Dark Matter Halos

摘要： 我们使用N体/气体动力学Λ冷暗物质宇宙学模拟来研究星系聚合对其暗晕形状和质量分布的影响。比较了两组模拟：一组仅跟踪暗物质成分的演化，另一组加入了重子成分。这些模拟包括辐射冷却但忽略了恒星形成和反馈，导致大多数重子聚集在太小且过量的盘状结构中，与典型的螺旋星系相比显得不现实。尽管如此，这种不现实的模型仍使我们能够评估星系可能对暗晕产生的最大影响。我们发现暗晕变得更加轴对称：从三轴系统转变为本质上扁球形的系统，其等势面的拉长程度大致恒定（c/a ≈ 0.85）。由于星系聚合，暗晕总是会收缩，但其效果远不如“绝热收缩”假设预测的那么显著。减少的收缩有助于协调Λ冷暗物质晕与太阳圈内暗物质含量的限制，并应能缓解长期以来同时匹配星系盘的尺度属性和亮度函数的难题。暗晕的收缩程度也比早期模拟中发现的要小，这一分歧表明暗晕收缩不仅仅取决于重子的初始和最终分布。不仅暗晕中心沉积的重子质量多少起作用，沉积的方式也很重要。如果不深入了解一个星系的聚合历史，可能无法预测暗晕的响应。 显示英文摘要

摘要： We use N-body/gasdynamical LambdaCDM cosmological simulations to examine the effect of the assembly of a central galaxy on the shape and mass profile of its dark halo. Two series of simulations are compared; one that follows only the evolution of the dark matter component and a second one where a baryonic component is added. These simulations include radiative cooling but neglect star formation and feedback, leading most baryons to collect at the halo center in a disk which is too small and too massive when compared with typical spiral. This unrealistic model allows us, nevertheless, to gauge the maximum effect that galaxies may have in transforming their dark halos. We find that the shape of the halo becomes more axisymmetric: halos are transformed from triaxial into essentially oblate systems, with well-aligned isopotential contours of roughly constant flattening (c/a ~ 0.85). Halos always contract as a result of galaxy assembly, but the effect is substantially less pronounced than predicted by the "adiabatic contraction" hypothesis. The reduced contraction helps to reconcile LambdaCDM halos with constraints on the dark matter content inside the solar circle and should alleviate the long-standing difficulty of matching simultaneously the scaling properties of galaxy disks and the luminosity function. The halo contraction is also less pronounced than found in earlier simulations, a disagreement that suggests that halo contraction is not solely a function of the initial and final distribution of baryons. Not only how much baryonic mass has been deposited at the center of a halo matters, but also the mode of its deposition. It might prove impossible to predict the halo response without a detailed understanding of a galaxy's assembly history. (Abriged)