The coherent motion of Cen A dwarf satellite galaxies remains a challenge for $\Lambda$CDM cosmology

TL;DR

The paper investigates the persistent challenge of the plane-of-satellites problem in $ ext{Lambda}$CDM cosmology by analyzing the coherent motion of Cen A dwarf satellites, revealing such structures are rare in simulations and difficult to reproduce.

Contribution

This study adds new observational data on Cen A's satellite system and compares it with cosmological simulations, highlighting the rarity and transient nature of such coherent structures.

Findings

21 out of 28 satellites share coherent motion

Such structures are found in only 0.2% of Cen A analogs in simulations

Simulated structures are short-lived and often due to chance projection

Abstract

The plane-of-satellites problem is one of the most severe small-scale challenges for the standard $\Lambda$CDM cosmological model: several dwarf galaxies around the Milky Way and Andromeda co-orbit in thin, planar structures. A similar case has been identified around the nearby elliptical galaxy Centaurus A (Cen A). In this Letter, we study the satellite system of Cen A adding twelve new galaxies with line-of-sight velocities from VLT/MUSE observations. We find 21 out of 28 dwarf galaxies with measured velocities share a coherent motion. Similarly flattened and coherently moving structures are found only in 0.2% of Cen A analogs in the Illustris-TNG100 cosmological simulation, independently of whether we use its dark-matter-only or hydrodynamical run. These analogs are not co-orbiting, and arise only by chance projection, thus they are short-lived structures in such simulations. Our findings indicate that the observed co-rotating planes of satellites are a persistent challenge for $\Lambda$CDM, which is largely independent from baryon physics.