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

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 ${\hat{e}}_{3}$ eigenvector) are strong at early times, feeding the so-called ${\hat{e}}_{3}$ -structure, while the smallest TOI axis rapidly decreases. The ${\hat{e}}_{3}$ -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 ${\hat{e}}_{3}$ are those whose orbital poles are either aligned from early times or have been successfully bent at ${\hat{e}}_{3}$ -structure collapse. KPP satellites associated with ${\hat{e}}_{1}$ tend to have early trajectories already parallel to ${\hat{e}}_{3}$ . 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.