Breaking the Disk-Halo Degeneracy at Low Surface-Brightness

这项由威斯康星大学麦迪逊分校的Matthew Bershady博士承担的项目的主要目的是通过直接的运动学测量，独立地确定附近低表面亮度螺旋星系的盘状和晕组分的质量分布。科学动机是了解这些系统是否真的是所有半径的暗物质主导，精确地测量它们圆盘的质量与光的比率，并确定这对它们的恒星种群有什么影响。伯沙迪博士还试图对盘状恒星初始质量函数设置极限，并测试修正牛顿引力的非牛顿极限假设的可行性。测试将通过旋转曲线分解进行，该分解使用测量的磁盘质量与光比，并使用测量的磁盘垂直加速度来查看磁盘光是否跟踪磁盘质量。该技术方法利用观测到的恒星视线速度弥散(LOSVD)实现了一种替代方法，即通过气体和恒星切向速度估计10-15个低表面亮度星系的LOSVD。这些观测将在几台大型望远镜上进行，使用伯沙迪博士开发的新的和升级的整场光谱分析仪器。该计划包括(1)研究生和本科生培训，扩展到南非代表性较低的群体；(2)星系形成和光谱分析仪器的课程开发将与研究工作交织在一起；(3)委托进行新仪器的科学项目；以及(4)关于伯沙迪博士研究的公共外联讲座。程序的设计和执行涉及三年时间内的数据收集、建模和分析。

The main purpose of this project, undertaken by Dr. Matthew Bershady of the University of Wisconsin at Madison, is to determine independently the mass distributions of the disk and halo components of nearby, low surface-brightness spiral galaxies through direct, kinematic measurements. The scientific motivation is to understand if such systems are truly dark-matter dominated at all radii, to measure precisely the mass-to-light ratios of their disks, and to determine what implications this has for their stellar populations. Dr. Bershady also seeks to place limits on the disk stellar initial mass function and test the viability of the hypothesis of non-Newtonian limit of modified Newtonian gravity. Tests will be carried out via rotation-curve decompositions that use the measured disk mass-to-light ratios, and by using the measured disk vertical acceleration to see if disk light traces disk mass. The technical approach uses observed stellar line-of-sight velocity dispersions (LOSVDs) to implement a surrogate method of estimating LOSVDs in 10-15 low surface-brightness galaxies via gas and stellar tangential velocities. The observations will be carried out at several large telescopes, with new and upgraded integral-field spectroscopic instruments developed by Dr. Bershady.The program includes (1) graduate and undergraduate training, extended to under represented groups in South Africa, (2) course development on galaxy formation and spectrograph instrumentation will intertwine with the research work, (3) commissioning science programs on new instruments, and (4) public outreach lectures on Dr. Bershady's research. The program design and execution involve data collection, modeling and analysis over a three-year period.