Identifying Contributions to the Stellar Halo from Accreted, Kicked-Out, and In Situ Populations
Allyson A. Sheffield, Steven R. Majewski, Kathryn V. Johnston, Katia Cunha, Verne V. Smith, Andrew M. Cheung, Christina M. Hampton, Trevor J. David, Rachel Wagn… 展开作者
Allyson A. Sheffield, Steven R. Majewski, Kathryn V. Johnston, Katia Cunha, Verne V. Smith, Andrew M. Cheung, Christina M. Hampton, Trevor J. David, Rachel Wagner-Kaiser, Marshall C. Johnson, Evan Kaplan, Jacob Miller, Richard J. Patterson
[Abridged] We present a medium-resolution spectroscopic survey of late-type giant stars at mid-Galactic latitudes of (30$^{\circ}<|b|<60^{\circ}$), designed to probe the properties of this population to distances of $\sim$9 kpc. Because M giants are generally metal-rich and we have limited contamination from thin disk stars by the latitude selection, most of the stars in the survey are expected to be members of the thick disk ($<$[Fe/H]$>\sim$-0.6) with some contribution from the metal-rich component of the nearby halo.
Here we report first results for 1799 stars. The distribution of radial velocity (RV) as a function of l for these stars shows (1) the expected thick disk population and (2) local metal-rich halo stars moving at high speeds relative to the disk, that in some cases form distinct sequences in RV-$l$ space. High-resolution echelle spectra taken for 34 of these "RV outliers" reveal the following patterns across the [Ti/Fe]-[Fe/H] plane: seventeen of the stars have abundances reminiscent of the populations present in dwarf satellites of the Milky Way; eight have abundances coincident with those of the Galactic disk and more metal-rich halo; and nine of the stars fall on the locus defined by the majority of stars in the halo. The chemical abundance trends of the RV outliers suggest that this sample consists predominantly of stars accreted from infalling dwarf galaxies. A smaller fraction of stars in the RV outlier sample may have been formed in the inner Galaxy and subsequently kicked to higher eccentricity orbits, but the sample is not large enough to distinguish conclusively between this interpretation and the alternative that these stars represent the tail of the velocity distribution of the thick disk. Our data do not rule out the possibility that a minority of the sample could have formed from gas {\it in situ} on their current orbits.
Accreted stars and stellar haloes of simulated galaxies in TNG50
Facultad de Matemática, Astronomía, Física y Computación, UNC（数学、天文学、物理与计算科学学院，科尔多瓦国立大学）；Instituto de Astronomía Teórica y Experimental, CONICET–UNC（理论与实验天体物理研究所，阿根廷国家科学研究委员会-科尔多瓦国立大学）；Observatorio Astronómico de Córdoba, UNC（科尔多瓦天文台，科尔多瓦国立大学）；Department of Physics and Astronomy, University of Victoria（物理学与天文学系，维多利亚大学）
A Walk on the Retrograde Side (WRS) project. II. Chemistry to disentangle in situ and accreted components in Thamnos
INAF - Astrophysics and Space Science Observatory of Bologna（意大利国家天体物理研究所博洛尼亚天文与空间科学观测站）；Department of Physics and Astronomy, University of Bologna（博洛尼亚大学物理与天文学系）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）
The Milky Way has no in-situ halo other than the heated thick disc. Composition of the stellar halo and age-dating the last significant merger with Gaia DR2 and APOGEE
A Tale of Two Origins: In-Situ versus Accreted Nitrogen-Rich Field Stars in the MW
School of Physics and Astronomy, Sun Yat-sen University（中山大学物理学院）；CSST Science Center for the Guangdong-Hong Kong-Macau Greater Bay Area（粤港澳大湾区嫦娥科学中心）；Universidad Católica del Norte（北天主教学会大学）；Department of Astronomy, AlbaNova University Center, Stockholm University（斯德哥尔摩大学阿尔巴诺瓦大学中心天文学系）；Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉古纳大学天体物理学系）；CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台光学天文重点实验室）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）
Optimized HDBSCAN clustering for reconstructing the merger history of the Milky Way: applications and limitations
Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；School of Computer Science and Mathematics, Liverpool John Moores University（利物浦约翰摩尔斯大学计算机科学与数学学院）
Exoplanets in ancient stellar populations: occurrence constraints and hot-Jupiter candidates in the Galactic halo
University of Cambridge（剑桥大学）；University of British Columbia（不列颠哥伦比亚大学）；Caltech/IPAC-NASA Exoplanet Science Institute（加州理工学院/IPAC-NASA系外行星科学研究所）；Instituto de Astrofísica de Canarias (IAC)（加那利天体物理研究所）；Universidad de La Laguna (ULL)（拉帕鲁纳大学）；Tsinghua University（清华大学）；Nanjing University（南京大学）
Globular clusters in \textsc{OrbIT}: complete dynamical characterisation of the globular cluster population of the Milky Way through updated orbital reconstruction
Università degli Studi di Bologna（博洛尼亚大学）；INAF（意大利国家天体物理研究所）；Pontificia Universidad Católica de Chile（智利天主教 Pontificia 大学）；Instituto Milenio de Astrofísica MAS（MAS 天体物理研究所）；Université Côte d’Azur（蔚蓝海岸大学）；Observatoire de la Côte d’Azur（蔚蓝海岸天文台）
EDGE-INFERNO: The chemical signatures of assembly history in reionization fossils
American Museum of Natural History（美国自然历史博物馆）；University of Bath（巴斯大学）；University of Chicago（芝加哥大学）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙学物理研究所）；NSF-Simons AI Institute for the Sky (SkAI)（NSF-Simons 天空人工智能研究所 (SkAI)）；University of Surrey（萨里大学）；Lund University（隆德大学）；Carnegie Observatories（卡内基观测站）；Carnegie Theoretical Astrophysics Center, Carnegie Observatories（卡内基观测站卡内基理论天体物理学中心）；Columbia University（哥伦比亚大学）；Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森尼天体物理中心）
How well can we unravel the accreted constituents of the Milky Way stellar halo? A test on cosmological hydrodynamical simulations
Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉各拉纳大学）；Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）
University of Pennsylvania（宾夕法尼亚大学）；Lund University（隆德大学）；Carleton College（卡尔顿学院）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；City University of New York（纽约市立大学）
Cataloging Accreted Stars within Gaia DR2 using Deep Learning
这项研究的目标是提出一种基于机器学习的方法，该方法仅利用相空间将Gaia DR 2恒星分为两类：那些在银河系上吸积的恒星和原位的恒星。用于识别吸积恒星的传统选择方法通常依赖于完整的3D速度，金属丰度信息，或两者兼而有之，这大大减少了可分类恒星的数量。这里提倡的方法适用于Gaia DR 2的更大部分。一种被称为“迁移学习”的方法被证明是有效的，通过广泛的测试对一组模拟盖亚目录，是基于消防宇宙学放大银河系质量星系的流体动力学模拟。该机器首先使用仅5D运动学作为输入的模拟数据进行训练，然后在交叉匹配的Gaia/RAVE数据集上进行进一步训练，这提高了对真实银河系属性的敏感性。其结果是一个目录，确定了大约767，000颗Gaia DR 2内的吸积星。这个目录可以产生经验的见解合并历史的银河系，并可用于推断暗物质分布的属性。
