Probing Galaxy Potentials Using Orbital Dynamics

AST- 9803114 Sparke 星系中的大部分物质都是黑暗的，发出很少或根本没有光;我们只能从它的引力来推断它的存在。 任何半径内的总质量都可以从那里的圆形轨道上的气体速度推导出来;但是要找到暗晕的形状，或者有多少质量分布在其中，我们必须观察不止一个平面上的轨道，或者关于中心不对称的运动。 斯帕克博士正在研究观测到的恒星和气体运动与星系内质量分布之间的关系。 她正在使用极环系统进行部分工作。 在极环系统中，一个由气体、尘埃和恒星组成的环的轨道几乎与下面星系的赤道平面成直角。 她结合了在21厘米中性氢线上测量的环气运动，以及光学和近红外图像和光谱，来确定看不见的晕的平坦化。 她还在进行双杆势中星星和气体轨道的理论研究。 在许多棒星系中，可以在较大的主棒内看到一个较小的次级核棒;可能是中央棒的形状比较大的棒绕星系中心旋转得更快。 这项工作的另一部分是研究如何片面（即，星系盘与一个看不见的晕的中心不重合）可能会持续下去。 她有一个模型--引力n体--来跟踪这些偏离中心的圆盘的气体流动。 ***

AST- 9803114 Sparke Most of the mass in galaxies is dark, emitting little or no light; we infer the presence only from its gravitational force. The total mass within any radius can be deduced from the speed of gas in a circular orbit there; but to find the shape of the dark halo, or how much mass is distributed within it, we musst look at orbits in more than one plane, or motion which is not symmetric about the center. Dr. Sparke is studying the relation between the observed motions of stars and gas and the mass distribution within galaxies. She is using polar ring systems for part of this work. In polar ring systems, a ring of gas, dust and stars orbits almost at right angles to the equatorial plane of the underlying galaxy. She combines measurements of motions in the ring gas, made in the 21cm line of neutral hydrogen, with optical nad near-IR images and spectra, to determine the flattening of the unseen halo. She is also conducting a theoretical study of star and gas orbits in double-bar potentials. In many barred galaxies, a small secondary nuclear bar can be seen within the larger main bar; probably the figure of the central bar rotates more rapidly around the galaxy center than the larger bar. Another part of this work is the study of how lopsidedness (i.e., the disk of the galaxy does not coincide with the center of an unseen halo) might persist. She has a model - gravitational n-body - to follow the gas flow of these off-center disks. ***