📝 SummarXiv

Abstract

It has been suggested that the Plane of Satellites (PoS) phenomenon may imply a tension with current $\Lambda$CDM cosmology since a Milky-Way (MW)-like PoS is very rare in simulations. In this study, we analyze a large sample of satellite systems of MW-like galaxies in the IllustrisTNG simulations. We analyze their spatial aspect ratio, orbital pole dispersion, Gini coefficient, radial distribution, and bulk satellite velocity relative to the host galaxy. These are compared to the observed Milky~Way PoS. We identified galaxy samples in two mass ranges ($0.1 - 0.8 \times 10^{12} $ M$_\odot$ and $0.8 - 3.0 \times 10^{12}$ M$_\odot$). We find for both mass ranges that only $\sim$ 1 percent of MW-like galaxies contain a PoS similar to that of the MW. Nevertheless, these outliers occur naturally in $\Lambda$CDM cosmology. We analyze the formation, environment, and evolution of the PoS for nine systems that are most MW-like. We suggest that a PoS can form from one or more of at least five different processes. A massive Magellanic~Cloud (MC)-like satellite is found in 1/3 of the systems and probably plays an important role in the PoS formation. We find a tendency for about half of the satellites to have recently arrived at $z < 0.5$, indicating that a MW-like PoS is a recent and transient phenomenon. We also find that a spin up of the angular momentum amplitude of the most massive satellites is an indicator of the recent in-fall of the PoS satellites.