Is M31 at the center of its satellite system ?

TL;DR

This study investigates whether M31 is at the center of its satellite galaxy distribution, finding a possible slight offset but not statistically significant, emphasizing the need for more satellite discoveries to clarify the structure.

Contribution

The paper introduces a forward modeling approach that accounts for search completeness to assess M31's satellite distribution center relative to M31 itself.

Findings

Displacement of 10-50 kpc towards the Milky Way from M31's center.

Offset significance ranges from ≤1σ to 1.9σ, depending on assumptions.

Quadrupling known satellites could reveal a significant offset.

Abstract

The arrangement of M31's dwarf galaxies exhibits anisotropy, with the majority located in the hemisphere between the Milky Way and the host galaxy. This study aims to investigate whether M31's present location is aligned with the center of its distribution of dwarf galaxies. We use forward modeling to infer the center of the M31 satellite 3D spatial distribution, folding in the completeness of dwarf galaxy searches. We observe a displacement of the center of the satellite distribution, relative to the center of M31, of approximately 10--50 kpc towards the Milky Way. Nonetheless, the center of M31 remains compatible with the center of the dwarf galaxy distribution given the broad constraints on its position, with the significance of the shift ranging from $\leq 1\sigma$ to $1.9\sigma$, depending on the assumed form of the volumetric spatial distribution of satellites. If M31 is truly offset from its satellite system, a quadrupling of the number of known satellites would be necessary to infer a significant ($3\sigma$) offset. Hence, expanding the number of known dwarf galaxies is crucial to deepen our understanding of the distribution of M31 satellites and further shed on its peculiar structure.