Breaking the Disk-Halo Degeneracy at Low Surface-Brightness

该项目由麦迪逊的威斯康星州的Matthew Bershady博士承担，主要目的是通过直接的运动学测量，独立确定附近低表面亮度旋涡星系的盘和晕成分的质量分布。科学的动机是了解这样的系统是否真的在所有半径上都是暗物质占主导地位，精确测量其盘的质光比，并确定这对它们的恒星种群有什么影响。Bershady博士还试图对圆盘恒星初始质量函数进行限制，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，使用测量的磁盘质量与光的比率，并通过使用测量的磁盘垂直加速度，看看磁盘光跟踪磁盘质量。该技术方法使用观测到的恒星视线速度色散（LOSVDs），通过气体和恒星切向速度来实现估计10-15个低表面亮度星系中LOSVDs的替代方法。观测将在几个大型望远镜上进行，使用Bershady博士开发的新的和升级的积分场光谱仪器。该计划包括（1）研究生和本科生培训，扩展到南非的代表性不足的群体，（2）星系形成和光谱仪仪器的课程开发将与研究工作相结合，（3）委托新仪器的科学计划，以及（4）关于Bershady博士研究的公共推广讲座。该计划的设计和执行涉及三年内的数据收集，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.