Dark and luminous matter in the outer halos of elliptical galaxies

椭圆星系形成的大部分化石记录都隐藏在大半径内，那里的动力学时间很长，暗物质占主导地位，预计大部分角动量都存在。除了几个有效半径以外，研究恒星运动学的唯一示踪剂是行星星云(PNE)。对椭圆星系外晕的Pn运动学的调查结果表明，它们的动力学存在无法解释的二分性，仅从光度学角度看并不明显。动力学模型还表明，这些系统中的几个要么在五个有效半径内包含很少的暗物质，要么它们的恒星晕具有极大的径向轨道各向异性。相比之下，X射线明亮系统的模拟揭示了大质量和密集的暗物质晕，以及强烈的辐射偏向的恒星外部分布。为了更好地理解这些结果背后的原因，我们建议对X射线亮椭圆体和X射线弱椭圆体的精选样本建立动力学模型。该项目的目标是确定椭圆的角动量含量、轨道结构和暗物质含量作为光度和环境的函数，从而获得必要的信息，以区分在椭圆星系形成过程中起作用的不同合并过程。

Much of the fossil record of elliptical galaxy formation is hidden at large radii, where dynamical times are long, dark matter dominates, and most of the angular momentum is expected to reside. The only tracers for studying stellar kinematics beyond a few effective radii are planetary nebulae (PNe). Results from a survey of PN kinematics in the outer halos of elliptical galaxies have revealed an unexplained dichotomy in their dynamics, which is not apparent from photometry alone. Dynamical modeling has also shown that several of these systems either contain little dark matter within five effective radii, or that their stellar halos are characterized by extreme radial orbit anisotropy. By contrast, modeling of X-ray bright systems is revealing massive and dense dark matter halos, and a strongly radially biassed outer distribution of stars. In order to understand better what lies behind these results, we propose to construct dynamical models for a well-chosen sample of both X-ray bright and X-ray faint ellipticals. The goal of the project is to determine the angular momentum content, orbital structure, and dark matter content of ellipticals as a function of luminosity and environment, and thereby obtain the necessary information for distinguishing between the different merger processes at work in the formation of elliptical galaxies.