Hubble-constant and -mass determination of Centaurus A and M83 from tip-of-red-giant-branch distances

An independent determination of the Hubble constant is crucial in light of the persistent tension between early- and late-Universe measurements. In this study, we analysed the dynamics of the Centaurus A (CenA) and M83 galaxies, along with their associated dwarf companions identified via tip-of-the-red-giant-branch (TRGB) distance measurements, to constrain both the group mass and the local value of H 0 . By examining the motions of these galaxies relatively to the system’s barycentre, we applied both the minor and major infall models, which provide bounds on the true radial-velocity dispersion. From the overlap of these approaches, we obtain a virial mass estimate of (7.3 ± 2.0)×10 12 M ⊙ and a Hubble-flow-based mass of (2.6 ± 1.4)×10 12 M ⊙ . Modeling the cold Hubble flow around the group centre of mass, we derive a corresponding value of the Hubble constant as (64.0 ± 4.6) km s −1 Mpc −1 . These results offer an independent, dynamically motivated constraint on the local value of H 0 , explicitly accounting for the impact of peculiar velocities in the nearby Universe. We also discuss the ∼2 σ tension between the virial and Hubble-flow-based mass estimates, which likely arises from the fact that M83 is close to the velocity surface and goes against the Hubble-flow-model assumptions. While the Hubble-flow fit emphasises galaxies that follow smooth expansion on the lower branch of the velocity-distance relation, the virial mass estimate is found to be in good agreement with the group mass derived from the K -band luminosity of its brightest members and the projected mass methods.