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A large fraction of the dwarf satellites orbiting the Andromeda galaxy are surprisingly aligned in a thin, extended and apparently kinematically coherent planar structure. Such a structure is not easily found in simulations based on the Cold Dark Matter model ({Lambda}CDM). Using 21 high resolution cosmological simulations we analyse the kinematics of planes of satellites similar to the one around Andromeda. We find good agreement when co-rotation is characterized by the line-of-sight velocity. At the same time, when co-rotation is inferred by the angular momenta of the satellites, the planes are in agreement with the plane around our Galaxy. We find such planes to be common in our high concentration haloes. The number of co-rotating satellites obtained from the sign of the line-of-sight velocity shows large variations depending on the viewing angle and is consistent with that obtained from a sample with random velocities. We find that the clustering of angular momentum vectors of the satellites in the plane is a better measure of the kinematic coherence. Thus we conclude that the line-of- sight velocity is not well suited as a proxy for the kinematical coherence of the plane. Analysis of the kinematics of our planes shows a fraction of $sim$30% chance aligned satellites. Tracking the satellites in the plane back in time reveals that these planes are a transient feature and not kinematically coherent as would appear at first sight. Thus we expect some of the satellites in the plane around Andromeda to have high velocities perpendicular to the plane.
We use the APOSTLE $Lambda$CDM cosmological hydrodynamical simulations of the Local Group to study the recent accretion of massive satellites into the halo of Milky Way (MW)-sized galaxies. These systems are selected to be close analogues to the Larg
The dwarf galaxy NGC 3109 is receding 105 km/s faster than expected in a $Lambda$CDM timing argument analysis of the Local Group and external galaxy groups within 8 Mpc (Banik & Zhao 2018). If this few-body model accurately represents long-range inte
The spherical Jeans equation is a widely used tool for dynamical study of gravitating systems in astronomy. Here we test its efficacy in robustly weighing the mass of Milky Way analogues, given they need not be in equilibrium or even spherical. Utili
Dwarf satellite galaxies are thought to be the remnants of the population of primordial structures that coalesced to form giant galaxies like the Milky Way. An early analysis noted that dwarf galaxies may not be isotropically distributed around our G
Tidal streams from existing and destroyed satellite galaxies populate the outer regions of the Andromeda galaxy (M31). This inhomogeneous debris can be studied without many of the obstacles that plague Milky Way research. We review the history of tid