We study the incidence of group and filamentary dwarf galaxy accretion into Milky Way (MW) mass haloes using two types of hydrodynamical simulations: EAGLE, which resolves a large cosmological volume, and the AURIGA suite, which are very high resolution zoom-in simulations of individual MW-sized haloes. The present-day 11 most massive satellites are predominantly (75%) accreted in single events, 14% in pairs and 6% in triplets, with higher group multiplicities being unlikely. Group accretion becomes more common for fainter satellites, with 60% of the top 50 satellites accreted singly, 12% in pairs, and 28% in richer groups. A group similar in stellar mass to the Large Magellanic Cloud (LMC) would bring on average 15 members with stellar mass larger than $10^4{~\rm M_\odot}$. Half of the top 11 satellites are accreted along the two richest filaments. The accretion of dwarf galaxies is highly anisotropic, taking place preferentially perpendicular to the halo minor axis, and, within this plane, preferentially along the halo major axis. The satellite entry points tend to be aligned with the present-day central galaxy disc and satellite plane, but to a lesser extent than with the halo shape. Dwarfs accreted in groups or along the richest filament have entry points that show an even larger degree of alignment with the host halo than the full satellite population. We also find that having most satellites accreted as a single group or along a single filament is unlikely to explain the MW disc of satellites.
Anisotropy of Satellite Galaxies-I: Contrasting Correlations with Central Galaxy, Host Halo, and Large-Scale Filament Structures
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；College of Astronomy and Space Sciences, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Universidad Autónoma de Madrid（马德里自治大学）；Centro de Investigación Avanzada en Física Fundamental (CIAFF), Universidad Autónoma de Madrid（马德里自治大学基础物理前沿研究中心）；Institute for Astronomy, University of Edinburgh（爱丁堡大学天体物理研究所）；Department of Physics and Astronomy, University of the Western Cape（西开普大学物理与天文学系）；Observatoire Astronomique de Strasbourg, UMR 7550, CNRS, Université de Strasbourg（斯特拉斯堡天文台）
The Masses of the Milky Way and Andromeda galaxies
我们提出了一个家庭的强大的示踪剂质量估计计算封闭的质量的星系晕从离散的位置和运动学数据的示踪剂，如晕星，球状星团和矮卫星的样本。数据可以是投影位置、距离、视线速度或自行。给出了适合于银河系和M31的估计量的形式。蒙特卡罗模拟用于量化作为样本量函数的不确定性。对于银河系，卫星样本由26个具有视线速度的星系组成。我们发现，假设速度各向同性，300 kpc以内的银河系质量约为0.9 x 10^12太阳质量。然而，质量估计对各向异性很敏感，可能介于0.7 - 3.4 x 10^12太阳质量之间。将6颗银河系卫星的自行纳入数据集，我们发现约1.4 x 10^12太阳质量。如果使用合理的各向异性，这里的范围更广，从1.2 - 2.7 x 10^12太阳质量。对于M31，有23个卫星星系有观测到的视线速度，但只有M33和IC 10有自行。我们利用卫星星系的视速度和距离估算出M31在300 kpc以内的质量约为1.4 x 10^12太阳质量（假设各向同性）。它对各向异性的依赖性很小，质量在1.3 - 1.6 x 10^12太阳质量之间变化。考虑到不确定性，我们得出结论，卫星数据本身并不能可靠地了解这两个星系中哪一个质量更大。
Anisotropy of Satellite Galaxies-II: Spatial Segregation as the Origin of Anisotropic Satellite Quenching in Haloes and Beyond
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；College of Astronomy and Space Sciences, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Universidad Autónoma de Madrid（马德里自治大学）；Centro de Investigación Avanzada en Física Fundamental (CIAFF), Universidad Autónoma de Madrid（马德里自治大学基础物理前沿研究中心）；Institute for Astronomy, University of Edinburgh（爱丁堡大学天体物理研究所）；Department of Physics and Astronomy, University of the Western Cape（西开普大学物理与天文学系）
