Mapping the Milky Way Outer Halo with SEGUE and BOSS

使用 SEGUE 和 BOSS 绘制银河系外光环

• 批准号: 1009886
• 负责人: Heather Morrison
• 金额: $ 39.24万
• 依托单位: Case Western Reserve University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1009886&HistoricalAwards=false
• 关键词: Mapping; Milky; Way; Outer; Halo

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.

这项工作分析了大规模的形态和银河系晕的成分，发现，表征和映射的红巨星和蓝色水平分支（BHB）星在斯隆数字巡天（SDSS）地区。该分析使用了斯隆银河系理解和探索扩展巡天I和II（SEGUE I+II）中多达12，000颗K巨星，其中包括数百颗距离约150 kpc的发光K巨星。晕结构的详细地图与场星，而不是球状星团或流。椭圆星系的结构已经用场星进行了研究，但对于银河系还没有做太多的研究。其他使用球状星团和矮球状（dSph）星系的研究也很重要，但使用场星给出的银河系晕的图像偏差较小。这些恒星构成了银河系晕的大部分质量，其他星系的晕也是如此。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恒星分组为块和流。重子振荡光谱巡天（BOSS）将增加更多的K巨星。来自SEGUE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（相对铁氢比）或α元素的比例（例如，氧、硅、钙）相对于铁。如果调查所得光谱不能提供可靠数据，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产生精确的距离，因此有必要跟踪望远镜的时间，以单独瞄准这些恒星。结合动力学和化学信息，可以更好地了解银河系晕的组成，以及晕是如何组装的。与其他星系如M31的比较可以提供关于星系形成的进一步见解。一旦外晕的密度分布被绘制出来，BHB和巨星就被用作示踪剂来研究外晕的性质和历史。这可以与内晕的性质相比较，内晕被怀疑与外晕不同地进化。一个重要的测量是确定银河系的质量，从银河系中心到这些大半径。更广泛的影响：PI已经参与了SDSS光谱数据管道的校准几年，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。案例天文学正在与菲斯克/范德比尔特少数民族硕士桥梁计划合作，首席研究员积极参与这一伙伴关系。PI一直致力于本科教学，公共宣传和指导少数民族和妇女从事科学研究。