Dissecting the Sub-Structured Halo

Steven Majewski博士(弗吉尼亚大学)和他的团队将进行一系列五项主要实验，既将扩大已知银河系晕潮流的普查，又将利用晕流来了解星系的演化、结构形成和星系尺度上的暗物质(DM)。这些实验是(1)利用流星在光学和近红外波长的梯形光谱学研究晕潮流的化学，以证实在人马座流的前臂发现了金属丰度梯度；(2)研究流星的三维运动，该研究包含在54个近赤道Kapteyn选定区域的地面自行测量中，以求出流轨道并限制银河势的形状和强度，(3)利用绿洲望远镜对潮流中的M型巨星样本进行试验性研究，以寻找可用于潮汐气流精密天体测量的明亮的水脉泽，(4)光度学网格巨星调查的光谱后续活动，该巡天已确定一些先前已知和新发现的跨天半球的晕子结构，以及(5)更全面地描述G和K巨星的空间和径向速度分布，这似乎是该研究小组在大小麦哲伦云周围发现的“经典”恒星晕。我们银河晕的恒星成分为星系形成理论提供了一个重要的试验台。目前的“和谐”、分层次的DM宇宙学预测，恒星流的存在将是吸积的次晕的潮汐残留物。因此，找到并表征这些流提供了关键信息，以限制冷DM预测的合并历史的性质。这些流也是高度灵敏的动力学探测器，限制了银河系光晕的形状、强度和块度，并提供了对星系化学演化的关键见解。这项研究的一个关键方面是，它主要是由本科生和研究生的学生领导力和贡献推动的。作为博士论文的一部分，每个实验都由或将由不同的研究生领导。

Dr. Steven Majewski (University of Virginia) and his team will undertake a suite of five major experiments that will both expand the census of known Milky Way halo tidal streams and exploit halo streams for the understanding of galaxy evolution, structure formation and dark matter (DM) on galaxy-scales. These experiments are (1) A study of the chemistry of halo tidal streams using echelle spectroscopy of stream stars at both optical and near-infrared wavelengths to verify the discovery of a metallicity gradient in the leading arm of the Sagittarius stream, (2) A study of the 3-D motions of stream stars contained in a ground-based proper motion survey of 54 near-equatorial Kapteyn Selected Area fields to derive stream orbits and constrain the shape and strength of the Milky Way potential, (3) Undertake a pilot study with the Green Bank Telescope of a sample of M-type giant stars in tidal streams to look for bright water masers that can be used for precision astrometry of tidal streams using the Very Large Baseline Array, (4) A spectroscopic follow-up to the photometric Grid Giant Star Survey, which has already identified a number of previously known and newly discovered halo substructures across both hemispheres of the sky, and (5) More fully characterize the spatial and radial velocity distributions of G and K giant stars in what look to be "classical" stellar halos discovered around the Large and Small Magellanic Clouds by this research group. The stellar component of our Galactic halo provides an important test-bed for theories of galaxy formation. The present "concordance", hierarchical DM cosmologies predict the presence of stellar streams as tidal remnants of accreted sub-halos. Finding and characterizing these streams thus provides crucial information to constrain the nature of the Cold DM-predicted merging history. These streams are also highly sensitive dynamical probes constraining the shape, strength and lumpiness of the halo of the Milky Way, and provide key insights into the chemical evolution of galaxies. A key aspect of this research is that it has been fueled primarily by student leadership and contributions at both the undergraduate and graduate level. Each experiment is being led or will be led by a different graduate student as part of their Ph.D. dissertation.