Breaking the Disk-Halo Degeneracy at Low Surface-Brightness

这个项目由威斯康星大学麦迪逊分校的马修·伯沙迪博士承担，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螺旋星系的盘状和晕状成分的质量分布。科学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主导的，精确测量它们的圆盘的质量和光比，并确定这对它们的恒星数量有什么影响。伯沙迪博士还试图对盘状恒星的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来进行，旋转曲线分解使用测量的磁盘质量和光比，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距速度色散（losvd）来实现一种替代方法，通过气体和恒星切向速度估算10-15个低表面亮度星系的losvd。观测将在几个大型望远镜上进行，这些望远镜将使用伯沙迪博士开发的新的和升级的积分场光谱仪器。该计划包括(1)研究生和本科生的培训，扩展到南非代表性不足的群体；(2)星系形成和光谱仪仪器的课程开发将与研究工作交织在一起；(3)委托新仪器的科学项目；(4)对Bershady博士的研究进行公开宣传讲座。该计划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.