Are Disks of Satellites Comprised of Tidal Dwarf Galaxies?

Michal Bílek,Ingo Thies,Benoit Famaey,Pavel Kroupa

doi:10.3390/galaxies9040100

Abstract

It was found that satellites of nearby galaxies can form flattened co-rotating structures called disks of satellites or planes of satellites. Their existence is not expected by the current galaxy formation simulations in the standard dark matter-based cosmology. On the contrary, modified gravity offers a promising alternative: the objects in the disks of satellites are tidal dwarf galaxies, that is, small galaxies that form from tidal tails of interacting galaxies. After introducing the topic, we review here our work on simulating the formation of the disks of satellites of the Milky Way and Andromeda galaxies. The initial conditions of the simulation were tuned to reproduce the observed positions, velocities and disk orientations of the galaxies. The simulation showed that the galaxies had a close flyby 6.8 Gyr ago. One of the tidal tails produced by the Milky Way was captured by Andromeda. It formed a cloud of particles resembling the disk of satellites at Andromeda by its size, orientation, rotation and mass. A hint of a disk of satellites was formed at the Milky Way too. In addition, the encounter induced a warp in the disk of the simulated Milky Way that resembles the real warp by its magnitude and orientation. We present here, for the first time, the proper motions of the members of the disk of satellites of Andromeda predicted by our simulation. Finally, we point out some of the remaining open questions which this hypothesis, for the formation of disks of satellites, brings up.

Highlights

Satellite systems of many nearby galaxies concentrate in flattened co-orbiting structures, the so-called disks of satellites
The satellite systems rarely have ellipticities as high as observed
For the Milky Way, it has been proposed that the disk-like distribution of the satellites is just apparent because a substantial fraction of satellites was discovered by the Sloan

Summary

Introduction

Satellite systems of many nearby galaxies concentrate in flattened co-orbiting structures, the so-called disks of satellites. The real significance of the fact that the distribution of the satellites of the Milky Way looks interesting for us is difficult to estimate but is certainly higher than that the satellites would form a plane. These would be some of the main questions that could be clarified by investigating the distribution of satellites around other galaxies. Other searches for satellite planes in distant galaxies use information about the radial velocity This allowed [25] to detect that the satellites of NGC 2750 co-rotate around their host.

Proposals to Explain the Existence of Disks of Satellites

Findings

The Simulation of B18