Collaborative Research: Probing Phase-Space Structure in the Galaxy - Kapteyn's Selected Areas

最近的大面积光度测量结果表明，银河系外晕包含吸积驱动的子结构。这些已知或假设的卫星吸积残留物的结构，具有长期的，连贯的潮汐特征，可以用来精确地模拟银河系的引力势，以及原始卫星的特征。然而，这样的建模研究受到了有限的可用的运动学数据在大角度沿着潮汐功能。虽然径向速度计划最近刚刚开始解决少数已知的银河系潮汐尾的这个问题，但还没有系统的调查开始解决横向（切向）速度（即，绝对自行），其中包含两倍的动力学信息。如果没有这些信息，动力学模型仍然受到很差的约束，因此仅限于描述一系列可能的事件，而不是提供真实的事件的准确描述。在这个合作项目中，耶鲁大学的Dana Dinescu博士和弗吉尼亚大学的Steven Maubernski博士将进行深入的，高精度绝对和相对自行测量，将在1906年卡普坦指定的银河系结构研究选定区域内对50多条视线进行采样;事实上，Kapteyn和他的同事们当时拍摄的照片底片将被用作第一个纪元的材料。目前的自行程序没有达到这样的精度在一个类似的幅度限制，因此在检测和表征遥远的晕子结构的限制。在即将到来的GAIA和SIM天体测量卫星任务之前，该项目的自行精度、深度和天空覆盖范围将不会被超越。这些任务的数据可能分别在2015年和2020年提供，而该项目的结果将在未来3-4年内提供。自行将得到补充的径向速度，距离和金属丰度的估计，从光度和光谱工作，以及重叠的调查，如2 MASS，QUEST，SDSS和RAVE。这些数据的预期应用的例子包括：1）确定高度模糊的麒麟座的范围和轨道运动，银道面上方和下方的反中心结构，2）描述人马座潮汐流的横向运动。3)探测和表征银河系晕中的额外子结构。4)确定磁场中众多厚盘和晕星的运动学性质作为银河中心距离的函数。只有少数深，精确的（光束型）自行数据集集中在银河场恒星，而不是一个球状星团或矮椭球。该项目将大大增加集束型数据集的数量，从而在50多个不同的视线范围内系统地探测我们的银河系。使该项目成为可能的是原来的60英寸山的组合。威尔逊望远镜板在1909年采取了匹配杜蓬特2.5米板，从而产生了90年基线的优秀板规模的材料。这项研究将有助于我们的银河系与其以前的卫星相互作用的准确模型，并有助于描述银河系卫星系统的特征。此外，碎片星的运动学数据有可能测量暗物质晕的块状度。这两个问题与冷暗物质模拟有关，目前这些模拟将暗物质晕的数量相对于银河系观测到的卫星数量高估了两个数量级。***

Recent results from large-area photometric surveys have shown that the Milky Way outer halo contains accretion-driven substructure. These structures of known or assumed remnants of satellite accretion, have long-lived, coherent tidal features that can be used to accurately model the Galactic gravitational potential, as well as the characteristics of the original satellite. However, such modeling studies have been limited by the meager available kinematical data over large angles along the tidal features. While radial-velocity programs have just recently begun to address this problem for the few known Galactic tidal tails, no systemic survey has begun to address the transverse (tangential) velocities (i.e., absolute proper motions), which contain twice as much dynamical information. Without this information, dynamical models remain poorly constrained, and therefore limited to describing merely a range of possible events, rather than providing an accurate description of the real event.In this collaborative project, Dr. Dana Dinescu at Yale University and Dr. Steven Majewski, at the University of Virginia, will undertake a deep, high-precision absolute and relative proper-motion survey that will sample more than 50 lines of sight in the Selected Areas designated by Kapteyn for Galactic structure studies in 1906; indeed, the photographic plates taken at that time by Kapteyn and colleagues will be used as first epoch material. Current proper-motion programs do not achieve this precision at a similar magnitude limit, and are thus limited in detecting and characterizing distant halo substructure. The combination of proper-motion precision, depth,and sky coverage of this project will not be surpassed until the upcoming astrometric satellitemissions GAIA and SIM. The data from these missions may be available in 2015 and 2020 respectively, while results from this project will be available in the next 3-4 years. The proper motions will be complemented by radial velocities, distance and metallicity estimates from photometric and spectroscopic work as well as from overlapping surveys like 2MASS, QUEST, SDSS and RAVE. Examples of intended applications of the data include: 1) Determining the extent and orbital motion of the highly obscured Monoceros, anticenter structure both above and below the Galactic plane, 2) Characterizing the transverse motion of the Sagittarius tidal streams. 3) Detecting and characterizing additional substructures in the halo of the Milky Way. 4) Determining the kinematical properties of the numerous thick disk and halo stars in the fields as a function of Galacto-centric distance. There are only a few deep, precise (pencil-beam-type) proper-motion data-sets that are centered on Galactic field stars rather than on a globular cluster or a dwarf spheroidal. This project will substantially increase the number of pencil-beam-type data-sets and therefore systematically probe our Galaxy in more than 50 distinct lines-of-sight. What makes the project possible is the combination of original 60-inch Mt. Wilson telescope plates taken in 1909 with matching Du Pont 2.5-m plates, thus yielding a 90 year baseline of excellent plate scale material. This research will contribute to an accurate model of the interaction of our Galaxy with its former satellites, and help characterize the Galaxy's satellite system. Also, the kinematical data of debris stars have the potential of measuring the lumpiness of the dark matter halo. These two issues are relevant for cold dark matter simulations that currently overpredict, by two orders of magnitude, the number of dark matter halos relative to the number of observed satellites of the Milky Way. ***