Collaborative Research: M31 Satellites Past and Present

合作研究：M31卫星的过去和现在ast 1010039， Puragra Guhathakurta，加州大学圣克鲁斯分校（领导）ast 1009882, Steven R. Majewski，弗吉尼亚大学主校区，ast 1009973, James Bullock，加州大学欧文分校这是对仙女座（M31）的矮星球（dSph）卫星形成和演化的全面研究。本星系群中的这些卫星包括已知最不明亮的星系，它们可以被探索，以测试在最小的暗物质晕和最早的时间里恒星形成的想法。为了了解当前和过去的M31卫星系统的动态、合并、组装、恒星形成和化学富集历史是如何在分层星系形成的一般范例的背景下融合在一起的，将M31卫星的已分解恒星群的大量数据集与最先进的星系模型相结合。研究人员将M31的数据与先前研究过的银河系的卫星和光晕数量进行了比较。银河系和M31都是螺旋星系，但有不同数量的卫星星系，需要找到一个解释。M31的附加数据对于评估解决方案非常重要。丢失卫星的问题？在λ -冷暗物质（CDM）模拟中，亚晕的数量被预测为比观测到的卫星数量还要多。到目前为止，银河系是唯一一个可以与模型进行比较的系统，当这项研究的结果可用时，模型将会改变。三位主要研究人员长期合作，他们在美国国家科学基金会的支持下启动了SPLASH（仙女座恒星光晕的光谱和光度景观）调查。这里使用的方法和技术在这次合作中得到了很好的确立。SPLASH调查使用了Keck II望远镜上的深度成像多目标光谱仪（DEIMOS）和基特峰国家天文台的4米望远镜与马赛克CCD宽视场成像仪。该调查扩展到研究仙女座系统更多卫星星系中的红巨星分支星。该小组已经从成像数据中选择了139个DEIMOS掩模（大约20,000个光谱）和M31红巨星候选者的光谱。目标是观察另外135个DEIMOS掩模，以获得每颗已知和任何新发现的M31 dSph卫星中100多颗红巨星的光谱。M33是一颗与M31相互作用的低光度圆盘卫星，它的光谱被认为有大约3000颗恒星；东北陆架上大约有1000颗恒星，这是过去M31卫星的潮汐碎片，与M31的巨大南流有关。其中一部分工作结合了光谱和光度诊断来有效地分离M31红巨星。此外，还可以测量精确的恒星速度，以得出矮星系和潮汐流中的速度色散，这两种星系和潮汐流都是运动学上较冷的子系统。从中分辨率共添加光谱测量元素丰度被用来约束M31卫星的化学富集/恒星形成历史。理论模型用于确定M31中每个矮卫星星系的暗物质质量，从而将观测结果置于宇宙学框架内。这将提供更多的数据来解释如何在λ - cdm宇宙学的背景下描述银河系和M31的演化。这项工作为星系系统测试λ - cdm宇宙学提供了另一个数据集。这将对其他领域产生广泛的影响。deimos衍生的化学丰度是恒星种群研究界感兴趣的。这里开发的新分析方法为在其他恒星系统中进行类似的研究提供了基础，包括下一代望远镜所瞄准的更遥远的星系。本科生参与研究活动，研究生为其论文完成部分项目。这将有助于培养下一代科学家。研究人员努力在K-12的教室里发言，并接触到代表性不足的高中生和本科生。关于著名的大螺旋星系仙女座星系的研究结果非常适合纳入团队成员定期进行的公开讲座和演示。

Collaborative Research: M31 Satellites Past and PresentAST 1010039, Puragra Guhathakurta, University of California-Santa Cruz (lead)AST-1009882, Steven R. Majewski, University of Virginia Main CampusAST-1009973, James Bullock, University of California-IrvineThis is a comprehensive study of the formation and evolution of the dwarf spheroidal (dSph) satellites of Andromeda (M31). These satellites within the Local Group include the least luminous galaxies known and they can be explored to test ideas about star formation in the smallest dark matter halos and at the earliest times.Extensive data sets on the resolved stellar populations of M31 satellites are combined with state-of-the-art galaxy models in order to learn how the dynamical -, merger -, assembly -, star formation -, and chemical enrichment histories of the current and past M31 satellite systems fit together in the context of the general paradigm of hierarchical galaxy formation. The data for M31 are compared to the satellites and halo population of the Milky Way galaxy for which were previously studied by the investigators. The Milky Way and M31 are both spiral galaxies but have different populations of satellite galaxies for which an explanations needs to be found. The additional data for M31 are important for evaluating solutions to the ?missing satellites problem? in Lambda-Cold Dark Matter (CDM) simulations, where the number of subhalos is predicted to be higher than the number of observed satellites. So far the Milky Way is the only system for which the comparison to models can be made which will change when the results of this study are available.The three principal investigators have a standing collaboration and they have initiated the SPLASH (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo) survey with previous support from the NSF. The methods and techniques used here are well established in this collaboration. The SPLASH survey uses the DEep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II telescope and the 4-m telescope with Mosaic CCD wide field Imager at Kitt Peak National Observatory. The survey extends to study red giant branch stars in more satellite galaxies of the Andromeda system. The group has already 139 DEIMOS masks (about 20,000 spectra) and spectroscopy of M31 red giant candidates selected from the imaging data. The goal is to observe another 135 DEIMOS masks to obtain spectra of more than 100 member red giant stars in each of the known and any newly found dSph satellites of M31. Further spectra are thought for about 3,000 stars in M33, a low-luminosity disk satellite interacting with M31; and about 1,000 stars in the NE shelf which is tidal debris from a past M31 satellite associated with the Giant Southern Stream in M31.One part of the work combines spectral and photometric diagnostics to isolate M31 red giants efficiently. Further there are measurements of precision stellar velocities to derive velocity dispersions in dwarf galaxies and tidal streams, which are both kinematically cold subsystems. Measurements of elemental abundances from moderate resolution co-added spectra tare used o constrain the chemical enrichment/star formation histories of M31 satellites. Theoretical models are used to determine the dark matter mass of each dwarf satellite galaxy in M31 to place the observations within a cosmological framework. This will give more data to decipher how the evolution of the Milky Way and M31 can be described in the context of Lambda-CDM cosmology.This work provides another data set for a galaxy system to test Lambda-CDM cosmologies. This will have a broad impact on other fields. The DEIMOS-derived chemical abundances are of interest for stellar population studies community. The new analytical methods developed here provide a foundation for similar studies of resolved stars in other stellar systems, including more distant galaxies to be targeted with the next generation of telescopes.Undergraduate students are participating in the research activities and graduate students work on parts of this project for their theses. This will help to train the next generation of scientists. The researchers make efforts to speak in K-12 classrooms and to reach out to underrepresented high-school and undergraduate students. Research results about the well-known large spiral galaxy Andromeda are well suited to be incorporated into public lectures and presentations which are given by the team members on a regular basis.