Zippers and Twisters: Planes of Satellite Galaxies Emerge from Whirling and Shocking Gas Streams in the Cosmic Web

Abstract We investigate dwarf satellite systems around massive centrals analogs (Milky Way to Centaurus A) in the NewHorizon simulation. Using simple estimators limiting overdetection, we identify planes of satellites comparable to observations in 30%–70% of cases. The full sample is strongly biased toward arrangements more elongated and corotating than their dark-matter hosts, as early as z = 1. We identify cosmic filaments and relics of local gas streams outside each system at z ≈ 0 with DisPerSE . We find that the thinner the local stream plane, the thinner the system is. The two align significantly for planar systems. Streams around isotropic systems are not planar. Our analysis reveals two plane types. Ultrathin planes lie orthogonally to their single nearest cosmic filament and align to coherent vortical flows within 3 Mpc, reminiscent of z > 2 whirls. A second group of planar systems align to their cosmic filaments. All planes are found in single cosmic filaments skirted by coherent vortical whirls, while isotropic systems are found in turbulent flows at the intersection of filaments. We conclude that planes are frequent in ΛCDM simulations, provided the cosmic environment is resolved. Tracking filaments back in time, we show a tight connection between a single, stable filament down to z ≈ 0 and the existence of a plane. “In-filament” planes typically get enhanced by a single, edge-on filament merger at z < 2 ( zipper ), while “vortical” planes’ filaments undergo single twisters (high-orbital momentum zippers), preventing the formation of a core along the filament. In contrast, isotropic systems’ filaments undergo multiple misaligned mergers.