The Origin of Kinematically Persistent Planes of Satellites as Driven by the Early Evolution of the Cosmic Web in ΛCDM

Abstract

Kinematically persistent planes (KPPs) of satellites are fixed sets of satellites co-orbiting around their host galaxy, whose orbital poles are conserved and clustered across long cosmic time intervals. They play the role of “skeletons,” ensuring the long-term durability of positional planes. We explore the physical processes behind their formation in terms of the dynamics of the local cosmic web (CW), characterized via the so-called Lagrangian volumes (LVs) built up around two zoom-in, cosmological hydro-simulations of Milky Way–mass disk galaxy + satellites systems, where three KPPs have been identified. By analyzing the LV deformations in terms of the reduced tensor of inertia (TOI), we find an outstanding alignment between the LV principal directions and the KPP satellites’ orbital poles. The most compressive local mass flows (along the eˆ3 eigenvector) are strong at early times, feeding the so-called eˆ3 -structure, while the smallest TOI axis rapidly decreases. The eˆ3 -structure collapse marks the end of this regime and is the timescale for the establishment of satellite orbital pole clustering when the Universe is ≲4 Gyr old. KPP protosatellites aligned with eˆ3 are those whose orbital poles are either aligned from early times or have been successfully bent at eˆ3 -structure collapse. KPP satellites associated with eˆ1 tend to have early trajectories already parallel to eˆ3 . We show that KPPs can arise as a result of the ΛCDM-predicted large-scale dynamics acting on particular sets of protosatellites, the same dynamics that shape the local CW environment.