Is M31 at the centre of its satellite system?

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 centre of its distribution of dwarf galaxies. We use forward modelling to infer the centre of the M31 satellite 3D spatial distribution, folding in the completeness of dwarf galaxy searches. We observe a displacement of the centre of the satellite distribution, relative to the centre of M31, of approximately 10–50 kpc towards the Milky Way. None the less, the centre of M31 remains compatible with the centre of the dwarf galaxy distribution given the broad constraints on its position, with the significance of the shift ranging from $\le 1\sigma$ 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.