Mapping the Milky Way Outer Halo with SEGUE and BOSS

这项工作通过在斯隆数字巡天(SDSS)区域发现、表征和绘制红巨星和蓝水平分支(BHB)星来分析银晕的大尺度形态和组成。这项分析使用了多达12,000颗来自斯隆扩展的K巨星，用于银河系理解和探索调查I和II(SEGUE I+II)，其中包括数百颗发光的K巨星，距离更大，最高可达150kpc。光晕结构是用场恒星而不是球状星团或流星详细映射的。椭圆星系的结构已经用场恒星研究过了，但对于银河系来说，这方面的研究还不多。其他使用球状星团和矮球星系(DSph)的研究也很重要，但使用场恒星可以给出一幅没有太多偏见的银河系晕图。这些恒星构成了银河系光晕的大部分质量，同样也构成了其他星系的光晕。在这里，大量的测试粒子(12,000颗恒星)应该提供了一个可靠的统计基础。这些恒星的径向速度测量被用来将这些恒星分组为团块和流。重子振荡光谱调查(BOSS)将增加更多的K巨星。来自恒星参数管道(SSPP)的K巨星数据也提供了这些恒星的化学信息，如金属丰度(相对铁与氢的比率)，或阿尔法元素(例如，氧、硅、钙)与铁的比率。如果调查的光谱没有提供可靠的数据，则进行其他后续光谱观测，以获得所需的丰度信息。BOSS或SEGUE-II光谱的信噪比可能不足以得出准确的距离，因此有必要跟踪望远镜的时间来单独瞄准这些恒星。结合动力学和化学信息可以更好地理解银晕的成分，以及晕是如何组装的。与M31等其他星系的比较可以提供对星系形成的进一步洞察。一旦绘制了外晕的密度分布图，就可以使用BHB和巨星作为示踪剂来研究外晕的性质和历史。这可以与内晕的性质进行比较，人们怀疑内晕的演化方式与外晕不同。一项重要的测量是从银河系中心到这些大半径的银河系的质量测定。广泛的影响：PI参与SDSS光谱数据管道的校准已经有几年了，是分析和理解这些数据的专家。这些数据在天文学界有很大的影响。这里的工作支持一名研究生和两名本科生。凯斯天文学正在与菲斯克/范德比尔特少数民族大师桥项目合作，首席研究员积极参与了这一合作伙伴关系。PI一直致力于本科生教学、公共宣传以及在科学研究中指导少数族裔和妇女。

This work analyzes the large-scale morphology and constituents of the Galactic halo by finding, characterizing, and mapping the red giant stars and blue horizontal branch (BHB) stars in the Sloan Digital Sky Survey (SDSS) region. The analysis uses as many as 12,000 K giant stars from the Sloan Extension for Galactic Understanding and Exploration surveys I and II (SEGUE I+II) including a few hundred luminous K giants with larger distances up to about 150 kpc. The halo structure is mapped in detail with field stars rather than globular clusters or streams. The structure of elliptical galaxies has been studied with field stars, but this has not been done much for the Milky Way. Other studies using globular clusters and dwarf spheroidal (dSph) galaxies are also important, but the use of field stars gives a less biased picture of the Milky Way halo. These stars make up most of the mass of the Milky Way halo, and similarly of the halos of other galaxies. Here the large number of test particles (12,000 stars) should provide a sound statistical base. Radial velocity measurements of these stars are used to group the stars into lumps and streams. More K giant stars will be added from the Baryon Oscillation Spectroscopic Survey (BOSS). Data for K giants from the SEGUE Stellar Parameter Pipeline (SSPP) also provide chemical information for these stars such as metallicity (the relative iron to hydrogen ratios), or the ratios of alpha elements (e.g., oxygen, silicon, calcium) relative to iron. Other follow-up spectroscopic observations are done to obtain the required abundance information if spectra from the surveys do not provide reliable data. The signal-to-noise ratio of BOSS or SEGUE-II spectra might be insufficient to yield accurate distances, and it becomes necessary to follow up with telescope time to target those stars individually.Combining the dynamical and chemical information leads to a better understanding of the Galactic halo components, and how the halo assembled. Comparisons to other galaxies such as M31 can provide further insights about galaxy formation. Once the density distribution of the outer halo is mapped, the BHB and giant stars are used as tracers to study the properties and history of the outer halo. This can be compared to properties of the inner halo, which is suspected to have evolved differently than the outer halo. One important measurement is the mass determination of the Milky Way out to these large radii from the Galactic center.Broader Impact: The PI has been involved with the calibration of the data pipelines for the SDSS spectra for several years and is an expert at analyzing and understanding these data. These data have a large impact in the astronomical community. The work here supports a graduate student and two undergraduate students. Case astronomy is partnering with the Fisk/Vanderbilt Masters Bridge Program for minorities, and the principal investigator is actively involved in this partnership. The PI has an ongoing commitment to undergraduate teaching, public outreach, and mentoring minorities and women in scientific research.