2026A&A...707L..10B

Centaurus A (Cen A) and M 83 form one of the most massive galaxy pairs in the nearby Universe. Although their observed heliocentric velocities suggest motion that is not obviously indicative of mutual attraction, this work presents evidence that Cen A and M 83 are in fact gravitationally attracted toward each other, exhibiting a dynamical interaction analogous to the binary-like motion of the Milky Way and Andromeda in the Local Group (LG). Using the timing argument, calibrated with analog galaxy pairs from the AbacusSummit simulation, we estimated the total mass of the Cen A/M83 system under the assumption that the line-of-sight velocity is dominated by motion toward the system's barycenter. This yields a total mass of (6.36 ± 1.30)⋅10¹² M_⊙. The inferred mass agrees well with independent estimates based on virial mass measurements and K-band luminosity-to-mass ratios. Together, the consistent bound signature and robust mass determination highlight the Cen A/M83 system as a compelling nearby analog to the LG. A further discussion of NGC 4945 as a main perturber (similar to the Large Magellanic Cloud for the LG) of Cen A is also presented.