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.

这项工作通过在斯隆数字天空调查（SDSS）地区找到，表征和绘制红色巨星和蓝色的水平分支（BHB）恒星来分析银河光环的大规模形态和成分。该分析使用了来自Sloan扩展的多达12,000 k巨星，用于银河理解和勘探I和II（SEGUE I+II），其中包括几百个发光的K巨人，距离较大，距离约为150 kpc。光环结构用田间恒星详细映射，而不是球状簇或流。椭圆星系的结构已经用田间恒星研究了，但是对于银河系而言，这并没有做太多。使用球状簇和矮球（DSPH）星系的其他研究也很重要，但是田间恒星的使用给出了银河系光环的偏见。这些恒星构成了银河系光环的大部分质量，同样是其他星系的光环。在这里，大量的测试颗粒（12,000颗恒星）应提供合理的统计基础。这些恒星的径向速度测量值用于将恒星分为团块和溪流。 Baryon振荡光谱调查（BOSS）将增加更多的K巨星。来自SEGUE Stellar参数管道（SSPP）的K巨人的数据还为这些恒星（例如金属性（相对铁与氢比）或相对于铁的Alpha元素（例如氧，硅，钙）的比率提供了化学信息。如果调查中的光谱不提供可靠的数据，则进行其他随访光谱观察以获取所需的丰度信息。 Boss或Segue-II光谱的信噪比可能不足以产生准确的距离，并且有必要跟进望远镜的时间来瞄准这些恒星，以将这些恒星单独瞄准，以更好地理解银河系光环组件的动力学和化学信息，从而可以更好地理解晕圈的组件，以及如何组装晕圈。与其他星系（例如M31）的比较可以提供有关星系形成的进一步见解。一旦映射了外晕的密度分布，BHB和巨星就被用作研究外晕的性质和历史的示踪剂。可以将其与内部光环的特性进行比较，后者疑似其演变与外光环的发展不同。一个重要的衡量方法是从银河中心对这些大半径的大量确定。Boader的影响：PI与SDSS光谱的数据管道的校准有关数年，并且是分析和理解这些数据的专家。这些数据对天文学界产生了很大的影响。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Fisk/Vanderbilt Masters Bridge计划合作，为少数民族提供了合作，主要研究人员正在积极参与此合作伙伴关系。 PI在科学研究中持续致力于本科教学，公共宣传以及少数群体和妇女的承诺。