Fig. 2: Satellite galaxy positions as seen from Andromeda.

This equal-area Aitoff sky projection in our adopted M31-centric coordinate system¹⁹ shows the expected positions of 37 M31 satellites, coloured according to their absolute magnitudes as compiled in ref. ¹⁸. Corresponding Monte Carlo distance uncertainties are drawn in black. Satellites with over a 50% chance of participating in M31’s satellite plane¹⁸ are drawn as circles and off-plane satellites are marked with triangles. The coloured smaller points each represent the direction of the most populated conical region with a given opening angle θ. The purple cross and line indicate the orientation and bounds of the hemispheric region (θ = 90°) that contains a maximum of 32 satellites, and the dashed purple line delineates a hemispheric region with 29 satellites locked in the direction of the Milky Way. The orange cross and line represent the orientation and bounds of the most significant cone (θ = 101°) containing 36 satellites, and the dashed orange line corresponds to the smallest cone also containing 36 satellites (θ = 106.5°) but oriented towards our Galaxy. The direction of the satellite distribution’s geometric centroid and mean resultant length (Supplementary Information) are shown as blue and red plus symbols. Andromeda’s satellite galaxies form a strongly asymmetrical distribution that is aligned towards the Milky Way.