The Distribution of Mass in Spiral Galaxies

螺旋星系包含恒星、气体和尘埃，它们集中在一个围绕星系中心缓慢旋转的薄圆盘上。这个由发光物质组成的圆盘嵌在一个由未知成分的不可见暗物质组成的扩展球形“晕”中。这种暗物质只能通过它对可观测的发光物质（如恒星和气体）的引力作用来揭示它的存在。暗物质和发光物质的相对数量在很大程度上是未知的。然而，通过仔细测量恒星的速度，可以推断出这些螺旋星系周围有多少暗物质。为了测量这些恒星的速度，波茨坦天体物理研究所建造了一台新仪器，与波茨坦多孔径分光光度计（PMAS）一起使用，该分光光度计安装在西班牙南部卡拉阿尔托天文台的3.5米望远镜上。

Spiral galaxies contain stars, gas, and dust, concentratedin a thin disk, which slowly rotates around the center of the galaxy. This disk of luminous matter is embedded in an extendedspherical so-called `halo´ of invisible dark matter of unknowncomposition. This dark matter reveals its presence only via itsgravitational pull on the observable luminous matter like the starsand gas. The relative amounts of dark and luminous matter is largelyunknown. However, by carefully measuring the velocities of the stars,it can be inferred how much dark matter surrounds these spiralgalaxies. To measure these stellar velocities, a new instrument isbuild at the Astrophysikalisches Institut Potsdam to be used with thePotsdam Multi-Aperture Spectrophotometer (PMAS) on the 3.5m telescopeof the Calar Alto observatory in southern Spain.