The potential role of NGC 205 in generating Andromeda's vast thin co-rotating plane of satellite galaxies

TL;DR

This study investigates whether the observed thin, co-rotating plane of satellite galaxies around Andromeda can result from a past close encounter with NGC 205, using N-body simulations and statistical analysis.

Contribution

It introduces a novel simulation-based scenario where NGC 205's interaction explains the formation of Andromeda's satellite plane, supported by probabilistic modeling.

Findings

Probability of reproducing observed thinness increased to ~0.01 at pericentre.

Simulated satellites' positions match observations with a maximum probability of 0.002.

Higher M31 mass and initial distribution extent slightly increase match probability.

Abstract

The Andromeda galaxy is observed to have a system of two large dwarf ellipticals and ~13 smaller satellite galaxies that are currently co-rotating in a thin plane, in addition to 2 counter-rotating satellite galaxies. We explored the consistency of those observations with a scenario where the majority of the co-rotating satellite galaxies originated from a subhalo group, where NGC 205 was the host and the satellite galaxies occupied dark matter sub-subhalos. We ran N-body simulations of a close encounter between NGC 205 and M31. In the simulations, NGC 205 was surrounded by massless particles to statistically sample the distribution of the sub-subhalos expected in a subhalo that has a mass similar to NGC 205. We made Monte Carlo samplings and found that, using a set of reference parameters, the probability of producing a thinner distribution of sub-subhalos than the observed NGC 205 + 15 smaller satellites (thus including the 2 counter-rotators, but excluding M32) increased from <1e-8 for the initial distribution to ~0.01 at pericentre. The probability of the simulated sub-subhalos occupying the locations of the observed co-rotating satellites in the line of sight velocity versus projected on-sky distance plane is at most 0.002 for 11 out of 13 satellites. Increasing the mass of M31 and the extent of the initial distribution of sub-subhalos gives a maximum probability of 0.004 for all 13 co-rotating satellites, but the probability of producing the thinness would drop to ~ 0.001.