Abstract
The plane-of-satellites problem is one of the most severe small-scale challenges for the standard Λ cold dark matter (ΛCDM) 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 that 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 they 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 ΛCDM, which is largely independent from baryon physics.
Highlights
One of the main challenges for current models of galaxy formation is the plane-of-satellites problem (Pawlowski 2018)
Our findings indicate that the observed co-rotating planes of satellites are a persistent challenge for Λ cold dark matter (ΛCDM), which is largely independent from baryon physics
In Müller et al (2021), we present spectroscopy taken with the Multi Unit Spectroscopic Explorer (MUSE) mounted at the Very Large Telescope (VLT) of 12 additional dwarf galaxies around Centaurus A (Cen A)
Summary
One of the main challenges for current models of galaxy formation is the plane-of-satellites problem (Pawlowski 2018). Kroupa et al (2005) pointed out that the flattened spatial distribution of the known eleven Milky Way satellites – a feature which was essentially discovered 40 years earlier – is incompatible with the standard Λ cold dark matter (ΛCDM) model of structure formation, which predicts nearly isotropic satellite distributions. This conclusion was met with several rebuttals (e.g., Zentner et al 2005; Libeskind et al 2005, 2009), showing that a certain degree. We use them to test our previous assessment of a co-rotating plane-ofsatellites around Cen A
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